Lara Croft and the Temple of Osiris is free for a short time on Steam.
Store Description:
Lara Croft and the Temple of Osiris is the sequel to the critically-acclaimed Lara Croft and the Guardian of Light, and the first-ever four-player co-op experience with Lara Croft.
Click here to get the game for free on Steam.
Expires 24th March.
Tomb Raider (2013), the origin story of the heroine, is also currently free: [Free Game] Tomb Raider (2013)