I believe that while steam has public APIs for most stuff but there’s no way for a 3rd party client to provide DRM authentication, so the majority of games will not launch unless you also have the official steam client installed (note that steam does have a cli client)., rendering any 3rd party apps either simple wrappers for steam or severely limited.
I know of this largely abandoned project: https://github.com/dmadisetti/steam-tui
I believe that while steam has public APIs for most stuff but there’s no way for a 3rd party client to provide DRM authentication, so the majority of games will not launch unless you also have the official steam client installed (note that steam does have a cli client)., rendering any 3rd party apps either simple wrappers for steam or severely limited.
That project does its job by running steamcmd, which is an official Valve client, not by calling public APIs.
That could be a viable way to implement parts of a Steam client, but since it depends on a proprietary tool, it wouldn’t be all open-source.
Edit: I wonder if Valve would be receptive to publishing the SteamCMD source code. They already have a github presence.