Welcome to our roundup of the best total conversion mods ever. Presented in no particular order, these are the mods that radically transform our favorite games into something different, with new and improved art, gameplay systems, locations, and adventures. Crafted through years of work, sometimes by large teams of volunteer modders, many of these mods have gone on to become PC gaming classics in their own right.

Here are the best total conversion mods ever made. 

Link: Sven Co-op on Steam

First released way back in 1999, Sven Co-op is still being both updated and played today. A cooperative mod for the original Half-Life, the mod allows groups of players to battle their way through the Half-Life campaign, where they'll find increased challenges and far more enemies, as well as new maps filled with puzzles and challenges. Over the years hundreds of new levels have been added along with new weapons, improved AI, and lots of customization options. Even if you don't own Half-Life, you can play it for free on Steam.

Link: A Game of Thrones mod site

For Game of Thrones fans, this mod is already at the top of your personal list or will be the moment you try it. It transforms CK II’s medieval Europe into the beautifully realised continents of Westeros and Essos and populates them with characters and events straight from the source material. Marry, mingle, or murder your way through the Starks, Lannisters and many other notable dynasties. Best of all, random game events will quickly spin the world into an enjoyable alt-reality of the fiction we’re so familiar with. This is an absolute must-have for gamers who are fans of the George RR Martin novels and the HBO series.

Link: Aliens TC ModDB page

Way back in 1994, this pioneer of full-conversion mods successfully recreated the 1986 sci-fi action film Aliens in Doom. It didn’t settle for just plopping face-huggers and aliens on a map, either: its custom levels mirror familiar locations and story beats from the film and even provide sound effects and voice clips lifted straight from the movie. Hearing Sergeant Apone through your headset reminding you to “Check those corners... check those corners!” not to mention Ripley furiously shouting “COME ON!” when climbing into her signature loader to do battle with the alien queen genuinely made me feel like I was part of the Aliens universe.

Link: Counter-strike ModDB page

You may have heard of it? The multiplayer Half-Life mod featured such team-based missions as hostage rescue and bomb defusal, each team with its own equipment and goals. With its quick rounds and exciting gunplay, Counter-Strike became an instant hit, and the community began creating maps of its own. Counter-Strike’s emphasis on teamwork and communication helped define a new genre of shooters, and the modders behind it were quickly hired by Valve.

Link: Nehrim site

Every full-conversion mod comes with a high degree of ambition, but it’s a truly special situation when the mod’s creators have the talent to match. Nehrim: At Fate’s Edge, created by German modding team SureAI over four years, does what the best full conversion mods do: reshapes the features that are lacking in the original game and provide hours of exciting new content. With original voice work by dozens of actors, big changes to several of the game’s familiar systems, and its own quests, story, lore, playable races, and a massive and beautifully designed new map to explore, Nehrim transforms The Elder Scrolls IV: Oblivion into an entirely new experience.

Link: Garry's Mod ModDB page

Plenty of games have a god mode accessible through console commands, but Garry’s Mod takes the idea to an entirely new level. A multiplayer sandbox limited only by your creativity, the mod has proven to be the ultimate tool for creating webcomics, videos and custom game modes, as it enables players to spawn objects and entities and pose them however they like. You can even play Half- Life 2 using all of the mod’s tools, turning Gordon Freeman from a simple gun-toting scientist into the ultimate expression of your will.

Link: Long War at Nexus Mods

Harder, longer, and with hundreds of changes to the base game, Long War extends XCOM's campaign, lets you play with up to 12 squad members at a time, adds new soldier classes, voice packs, weapons and technology, and lots of improved and completely overhauled systems. Long War wasn't just a hit with players but with XCOM's developers, who brought the mod team in to work on launch-day mods for XCOM 2, as well as create Long War 2.

Link: The Dark Mod site

This mod isn’t simply a celebration of the acclaimed Thief series using Doom 3’s engine, but actually an improvement on some of its features, especially the wonderful and engaging new lockpicking system. The open-ended stealth adventure lets you slink through a gorgeous, highly-detailed gothic steampunk world as you fill your pantaloons with loot and try to avoid detection. Most importantly, the mod comes with its own mission editor, enabling members of the community to create and submit their own custom levels and stories. The Dark Mod was released as a standalone game in 2013.

Link: Black Mesa site

It sounded like an impossible project: building the entirety of the celebrated FPS Half-Life in Half-Life 2’s Source engine, but after eight years of work by a large volunteer team of modders it finally became a reality. While it stops short of recreating the entire game (Gordon Freeman’s leap into Xen is the mod’s endpoint), it’s still a remarkable accomplishment. For Half-Life veterans it contains a mix of new design elements and familiar confrontations, and it’s a also great way to experience the ground-breaking adventure for those turned off by the dated graphics of the original.

Link: DayZ mod on Steam

In a game featuring starvation, sickness, and swarms of growling zombies, it still falls to other human players to provide most of the horror. While the standalone version of DayZ became a big hit in Early Access, the original open-world multiplayer survival mod is perfectly playable. The vast map and lack of global chat provide a feeling of intense loneliness, but the prospect of actually meeting someone else is a constant threat.

Link: Complex mod site

The name is certainly apt: this mod takes the real-time space strategy game and adds an almost absurd amount of complexity to nearly every single aspect. Alongside improvements to the AI, physics and graphics, the mod adds scores of new units and maps, constructible subsystems, deeper tech and research trees, and a diplomacy system. It even adds an actual calendar so gametime can be marked in years as in the Civilization series.

Link: Dota Allstars, a recent iteration of the original mod, worked on by IceFrog, who now works for Valve on Dota 2.

An exciting combination of RTS and RPG, the multiplayer battle arena mod for Warcraft III (based on a modded map from StarCraft) is a lot of things: simple to understand, difficult to master, and most of all, utterly addictive. In its early days DotA was a project that was passed from modder to modder, and like an unending stream of creeps it eventually spread through the gaming world to become a massive hit, as well as the first lanepushing game to have sponsored tournaments.

Link: NeoTokyo site

This team-based multiplayer mod for Half-Life 2 is set in a slick, futuristic cyberpunk city and features three different classes to choose from, each with their own distinct weapons and strengths. With lethally realistic gunfire and cloaking abilities available to some classes, NeoTokyo requires more stealthy and tactical play than many online shooters demand. Inspired by anime classics Ghost in the Shell and Akira, NeoTokyo also features an amazing and engrossing custom soundtrack that you’ll want to listen to even when you’re not playing the game. The mod was released as a standalone title in 2009.

Link: Mechwarrior: Living Legends site

Combining FPS action and simulation, this large scale multiplayer-only mod brings wonderfully realised Battletech mechs to life in Cryengine 2, though it began as a mod for Quake Wars. Tanks, jets, mechs and hovercraft strategically battle for territorial control in beautiful, varied, highlydetailed outdoor environments with full day/night cycles. The mod was so impressively made it was even sanctioned by Microsoft, who own the Mechwarrior franchise the mod is based on.

Link: Cry of Fear ModDB page

While it’s a standalone release now, Cry of Fear began as a Half-Life mod. It’s the story of a man who wakes after being hit by a car to discover his city is filled with gruesome monsters and his mind packed with psychological horrors. The mod has some interesting and immersive tweaks, such as an extremely limited inventory—and the fact that the game doesn’t pause while using it—that bring new challenges as you play through a disturbing, winding story with original animated sequences and multiple endings.

Link: Genkokujo ModDB page

The Sengoku period in Japan was a time of turmoil, political intrigue and near-constant warfare. What better time and place for a massive, openworld combat RPG built on the capable framework of Mount & Blade? The mod features actual clans and figures from Japanese history, new skins and armour types, new gunpowder weapons, and dozens of historically accurate locations spread across a map of Japan with twice the playable area of the original game. It also incorporates a number of other excellent M&B mods such as Diplomacy and Freelancer, which add even more great features.

Link: The Stanley Parable on Desura

You’re put in control of a clerk who suddenly finds himself completely alone at the office, but you’ll soon start to reconsider just how much control you actually have. While difficult to describe, the mod quickly proves to be a witty and insightful commentary on videogames, particularly the act of making choices. It’s also wonderfully narrated by a voice so soothing you’d like him to read you bedtime stories – if only you could trust him. It’s now a complete game with a lot more polish and an extended story, but the original mod remains a thoughtful, oddball delight.

Link: The Third Age on TWCenter

Every kid who ever picked up JRR Tolkien’s The Lord of the Rings novels has longed to step into Middle-earth, and one of the best ways to do it is with this mod for the turn-based strategy game Total War, capable as it is of portraying epic-scale battles. Third Age features over a hundred accurate locations and a dozen factions straight from the fiction. It includes custom units such as ents, trolls, giant spiders and wargs, and lets you play not just as heroes like the men of Gondor and the Silvan Elves, but also as the evil forces of Sauron’s Mordor, Isengard, and even the orcs of the Misty Mountains.

Link: Out of Hell ModDB page

As Donovan Ling, a lone cop investigating a garbled transmission from the industrial town of Grinwood, you quickly find yourself alone and fighting to survive a relentless zombie invasion. This mod is packed with astounding visuals of a city gone to hell, and a chilling original soundtrack accompanies you as you battle your way through more than 20 harrowing and atmospheric maps. Despite an arsenal of deadly weapons and melee attacks, you’ll never really have time to catch your breath.

Link: Natural Selection site

With one team playing marines and the other playing aliens, Natural Selection converts Half-Life into a multiplayer hybrid of first-person shooting and realtime strategy. It brought to life the concept of a commander in an FPS: a sole player who views the map in top-down fashion, giving orders, issuing supply drops, and managing the map in a traditional RTS fashion. The aliens have no overlord or shared resources, so must rely on communication if they want to win. Despite big differences in the two teams’ abilities and tactics, the mod remains a tightly balanced experience.

Link: Team Fortress ModDB page

Long before it evolved into a cartoony hat-trading simulation, Team Fortress was a mod for Quake. It originally featured five classes, later blossoming into the full iconic nine we’re familiar with today, and even provided a tenth class, the civilian, playable during VIP escort missions. Instead of just red and blue teams, certain maps for TF included two additional teams, green and yellow, struggling for map control and engaging in capture the flag games. The mod’s popularity led to a proper release and, much later, the Team Fortress 2 we know today, although the original mod is still played on a few servers.

Link: The Nameless Mod site

With a hundred new skins, sixty maps, custom cinematic sequences,and two storylines providing a hefty thirty hours of playtime, The Nameless Mod grew, over seven years of development, from something of an in-joke to a true mod masterpiece and Deus Ex fan favourite. Part homage and part satire, the mod sports thousands of lines of custom dialogue, tons of tweaks, and dozens of great new music tracks, not to mention books, newspapers and emails.