Good Old Games is offering a list of games for free on a landing page dedicated to reminding people to stay home.
Some publishers and developers are offering free games, and if you redeem them quickly, you get to keep them forever.
Itch.io,a platform primarily dedicated to small indies, also has a “Games to help you stay inside” page.
But starting March 20, 2020, you can hop over to Steam (or the official Square Enix Store) and get both Tomb Raider (2013) and Lara Croft and the Temple of Osiris.