Like Steam Desura is a client software Desura's online store that users need to install in order to download, install and play games. Like Steam it also manages game updates and has integrated community features. Desura is however unique in its community features that try to integrate game developers and players into the same network. It has brilliant modding support, using which one can even download and install mods for games not installed / purchased through Desura.
Unfortunately, these modding features are not available in the Linux client yet.
Linux isn't really a platform that is associated much with gaming but that impression is slowly changing as there are an increasing number of avenues for game developers to publish their gamers. Ubuntu has its own software store that has been selling games for quite a while now, and all the Humble Indie Bundles have been released across all platforms. Recently another gaming store called Gameolist was launched as well.
Now with the launch of Desura now adds yet another store for Linux gamers to buy games from. However there is another reason to be excited about Desura, and that is the fact that any game purchased through Desura is yours for all it supported platforms (just like SteamPlay which allows you to purchase a game once and play it on both Mac OSX and Windows if it is supported). So if you are a Windows user considering switching to Linux, you can buy the games now and they will continue to work on Linux. If you purchased any of the Humble Bundles, you can start playing those games on Linux via Desura already.
Currently of the over 200 games available on Desura, only around 65 are available for Linux; although this number will surely increase over time.
Desura is also looking to possibly open source their game client under GPL to allow the community to participate in developing that as well. Of course the server-side will remain closed. With an open source client, it is only a matter of time before one finds different versions of the Desura client with different approaches to packaging and downloading games, perhaps even integration with Wine to allow Linux users to play Windows-only games as well. It's something to look forward to.
Excited? Creating a Desura account is free and gives you access to a number of free / opens source games such as Xonotic, PlaneShift,Red Eclipse, Warsow, Alien Arena, StarFare and many more. Additionally, Desaura also has a number of Linux games on sale to celebrate he launch of their Linux Client. You can download the Desura client for your platform from here.