Game Jolt is a Steam-like service for indie games-- an easy way to find free or commercial games you like, then install, play and update them.
You can access Game Jolt from a browser, but Game Jolt Client enables using the service from a native desktop client. Okay, it's actually still a browser underneath (Chromium), but having a native client does mean it can integrate a little more with the operating system, and may be more convenient in some situations (you can restart your actual browser without closing a game).
If you know Game Jolt already there's not much to learn. Launch the program, log in and you can access your library or find new games as usual.
Game Jolt newbies will figure out the basics very quickly. Sign up with your email address to create an account, click "Games" and browse what's on offer. When we checked, the client listed "page 1 of 12,255 games", so there's plenty of choice.
Games either have "free" or their price displayed bottom-right. Click the thumbnail for any free game which looks interesting to read more about it, and click "Install" to download, install and play.
Other features include following games to get news, a "recommended games" area which suggests games you might like based on your current library, and even a chat client to message and get notifications from other Game Jolt members.