Free Offline FPS RPGs?

True free, offline, full FPS-RPGs are rare—development cost + no monetization = unsustainable. Closest options:

Free / Open Source

• Xonotic / OpenArena / Unvanquished: Arena FPS (Quake-style), not RPG.
• Revival (Project) / Gloome — Doom-engine RPGs, early.

Modded Classics (Best Experience)

• Half-Life 2 + Mods: SMOD Tactical, Entropy Zero 2 (story), Lambda Wars (RTS/FPS hybrid).
• Deus Ex (2000) + GMDX / Revision: Immersive sim/RPG, free mods, GOG version cheap.
• S.T.A.L.K.E.R. Anomaly / Gamma: Free standalone (own CoP), hardcore FPS-RPG, offline.
• Fallout 1/2 (GOG free sometimes) + Fixt/Restoration: Isometric, but deep RPG.

Indie / Low-Cost

• Dusk / Amid Evil / Ion Fury: Retro shooters, $20, no RPG systems.
• Borderlands 1/2/3 (Sales ~$10): Looter-shooter RPG, offline solo works.
• Destiny 2 (Free-to-play): Requires online.

Mobile

Dead Trigger 2 — FPS + RPG upgrades, but requires internet.

Best bet: Buy Deus Ex (GOG, ~$1) + GMDX mod or S.T.A.L.K.E.R. Anomaly (free, own CoP). True offline FPS-RPG depth.