While Conan Exiles technically has a dedicated server - it is exceptionally low quality, requiring a virtual framebuffer on Linux (it is not truly headless) and a highly complicated setup.

Has a freely available Dedicated Server for both Windows and Linux.

The server is downloadable via SteamCMD and accepts basic configuration via command line arguments, rest of the configuration is done via the games online portal or in-game admin commands.

While Unturned technically has a dedicated server - it is exceptionally low quality, requiring a virtual framebuffer on Linux (it is not truly headless) and a highly complicated setup.

Despite technically having dedicated servers (complete with a Steam repo) - they are not available to the general public.

Garrys Mod is easily downloadable using SteamCMD, and behaves like any other srcds based server such as the ones VALVe ship - with excellent configurability and remote admin capabilities.