You are in luck, Valve has SteamCMD[1] for users just like yourself! It is a command line version of the Steam client and can do most of what you need like downloading, updating, even verifying game integrity from the command line! I only wish it was open source, maybe someone can reverse engineer it?

[1] https://developer.valvesoftware.com/wiki/SteamCMD

Steam protocol has been well understood for a while now: https://github.com/steamre/steamkit

Which is based on reverse engineering the Steam client, so you can implement game downloading yourself.

It appears to be only for downloading/updating game servers; not for downloading/updating games.

but how do you run a game from that?

If it's possible someone can come up with a small UI that only lists and launches games.

Playnite [1]. Open source, lightning fast, and light on resources. You can even combine different platforms such as Steam + Battle.net. Saves you running each of these. Though you lose things like downloads and social. Heck, it even has support for emulators.

[1] https://playnite.link

From the article: https://github.com/DioJoestar/SteamCMD-GUI/blob/master/READM...

They don’t seem to have a *nix referral, but seems totally possible to make.

> Achievements, Trading cards/Inventory, Browser, Community, Workshop

Doesn't all of that work through embedded web-browser?

I think the embedded browser is where the most bloat is located. Although this particular vulnerability is not tied to it.

It work through a slow embedded web-browser.

Displaying achievements yes, but obtaining them has to interact in some ways with rest of the client. Trading cards and inventory probably too.

Valve's Steam uses VGUI toolkit (proprietary), and a WebKit-based embedded browser.