youronlyone , 
Here are some FLOSS/FOSS gaming–related official fediverse accounts (as listed on their official website(s)).
(in alphabetical order)
I. Game manager and playtime tracker
- Lutris — @lutris
II. FPS (First–person Shooter)
- Unvanquished (mix RTS+FPS) — @UNVofficial
III. MMOG (Massively Multiplayer Online Game)
- Crossfire — @crossfiremrpg
IV. Platformer
- SuperTux — @supertux
V. RTS (Real–time Strategy)
- 0 A.D. — @play0ad
VI. Sandbox
- Minetest — @Minetest
VII. Sim / Simulation
- OpenTTD (transport) — @openttd
- Simutrans (transport) — @simutrans
- Speed Dreams (racing) — @speed_dreams_official
VIII. TBS (Turn–based Strategy)
- FreeCiv — @freeciv
IX. TBT (Turn–based Tactics)
- The Battle for Wesnoth — @wesnoth
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