Inspired first-person puzzle game Portal is free to download on Steam until 20th September.

Maker Valve is running the deal to showcase how Portal and Portal 2 can and have helped kids grasp trickier aspects of science in an enjoyable way.

Apparently Portal makes things like physics and problem solving "cool and fun". And that "gets us one step closer to our goal: engaged, thoughtful kids!"

Portal, a short game, is a calm and bullet-free puzzle solving experience. Twists of humour and taxing, portal-based conundrums made it one of the best games of 2007.

Eurogamer's Portal review awarded 9/10.

Video: Portal finished in nine minutes. It's not always that short.

Square Enix will release the latest game from former Valve designer and Portal co-creator Kim Swift, with an official unveiling due this weekend.

The game, which Square's tease dubs "incredibly fascinating and quirky", is being developed at Dark Void developer Airtight Games, where Swift is now a project lead. We'll find out more about the title this Saturday at the PAX Prime show in Seattle.

Swift joined Valve straight out of Washington tech college DigiPen in 2005, where she co-developed Narbacular Drop - the direct inspiration for Portal's basic mechanics. As well as Portal, she also worked on Left 4 Dead 2 before leaving for Airtight back in December 2009.

Airtight's last effort, Capcom-published jet-pack actioner Dark Void, missed the mark when it launched back in January 2010, picking up a scrappy 5/10 from Eurogamer's Dan Pearson.

Few people will praise Portal higher than lead Brink writer Ed Stern.

During a Develop Conference talk he called Valve's creation "the greatest combination of premise, setting and player interaction we're ever likely to see".

Portal 1 came as part of The Orange Box in 2007. But the bite-sized compliment to Half-Life 2: Episode 2 and Team Fortress 2 quickly whipped up tumultuous applause of its own, scoring 9/10 in Eurogamer's Portal review. "One of the most interesting and delightful things Valve has ever done," Tom Bramwell wrote.

Portal 2 had big shoes to fill. But step into them it did, by earning 10/10 in Eurogamer's Portal 2 review. "It's a masterpiece," wrote Oli Welsh.

Ed Stern's comments about Portal were made answering whether Splash Damage overwrote Brink, a multiplayer-focused game.

"Brink is about frantic running and shooting, it's not exploring this world we've set up. It's a shooter," stated Stern.

"It's not about its setting in the same way that BioShock or Dragon Age or, God help us, Portal is. Portal, for my money, [is] the greatest combination of premise, setting and player interaction we're ever likely to see.

"All of this concepting and agonising and rewriting was for a shooter game that could have been red versus blue," Stern added. "Arguably we did not need a story in the first place."

Stern said Splash Damage chose a story because "we wanted to demonstrate as a story studio that we could do this stuff". Splash Damage wanted to add meaning to proceedings, although the mid-fight chaos often negated this.

"But I'm really glad we tried," said Stern. "I do not think Brink would have been a better game for having less world [built] into it."

Brink, released in May, tried to seamlessly weld single and multiplayer gameplay. Persist past its obtuse opening and you'll discover "an exceptional team shooter", wrote Simon Park in Eurogamer's Brink review - "smart, supremely well balanced and with a unique, exciting art style".

Video: Brink: PS3 versus Xbox 360.

Hours after releasing Portal 2 on Steam, creator Valve has announced predecessor Portal has sold close to four million units.

But Portal has likely sold substantially more copies. As GameSpot reports, the four million figure excludes digital download sales from Steam.

Portal launched in 2007 as part of the superb The Orange Box compilation.

In 2008 it launched as a standalone retail product. In the same year a version called Portal: Still Alive launched on Xbox Live Arcade.

Eurogamer's Portal review turned up a 9/10. "And so we're left with a curious contradiction: one of the most interesting and delightful things Valve's ever done, but also one of its least fulfilling," wrote Tom.

Thankfully, the sequel went one better. Eurogamer's Portal 2 review has all the details.

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On Valve's website sits a profile page, and on that profile page sits an entry for Left 4 Dead writer Chet Faliszek. It reads: "We are all still trying to figure out exactly what it is that Chet does at Valve, but at the very least he occupies office space on the 11th floor as self-proclaimed Mr. Awesome."

Mr. Awesome? Where does that come from?

"So our old HR person wrote that for me, and it was the example of a really bad profile to put up," Mr. Awesome told Eurogamer. "Then she wouldn't let me change it."

"The day of Half-Life: Episode 1," he continued, "that's where it came from. They were handing out recognition for Episode 1. No one knew what to say, so the first three or four people fumbled around. I just went up and I thanked myself for being awesome.

"Then other people who didn't know what to say just thanked me for being awesome."

So, what does Mr. Awesome do, apart from co-write alongside Erik Wolpaw on games such as Half-Life 2: Episode Two, Portal, Team Fortress 2, Left 4 Dead, Left 4 Dead 2 and the upcoming Portal 2?

"That description came after Half-Life: Episode 1. A lot of people didn't understand the part I played in that, with the response rules speech, which is on the fly speech.

"It was semi-accurate at the time. Now people know what I do. I walk around the hall with my iron fist, keeping people in line."

The Mr. Awesome description has been on Valve's website for five years. "I have to re-write it," Mr. Awesome said. "We don't even have an 11th floor anymore. We've moved buildings. But I don't want people to be able to find me."

Faliszek and writing partner Erik Wolpaw have been with Valve for six-and-a-half years. The duo, who grew up together, were hired after bumping into Valve through their website Old Man Murray.

"Out of the blue, in 2004, Gabe [Newell, Valve boss] just emailed us and said, do you want to come work for Valve?" Faliszek revealed.

"Gabe's initial email really was one line. We asked, can you explain more? "No. Just come out."

"I figured, what the hell," Wolpaw added. "We were just like, we'll just give it a shot and see what it's like. Seven years later, it's fine."

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