Silentium 2D

Yes. Silentium 2D is free to play on Steam, so there is nothing to buy to start playing.

The minimum requirements for Silentium 2D are: Windows XP, Intel Pentium 4, 512 MB RAM, 200 MB storage. It runs on Windows only. The recommended specs are in the System requirements section.

Yes. Silentium 2D has multiplayer and a single-player mode. It supports split-screen co-op and split-screen PvP.

Mostly, yes. Valve rates Silentium 2D as Playable on the Steam Deck: it runs, but may need some manual setup.

Yes. Silentium 2D is the full base game. You need nothing else to play it.