Arkane's 2017 Prey reboot has just hit GOG, and in-keeping with the mandate of that storefront, it's DRM free (opens in new tab). The dread-inducing immersive sim is also extraordinarily cheap for a limited time: it's $9 (or AU$13.49) for the standard edition.
While it didn't quite reach the heights of Arkane's Dishonored series, Prey was an excellent immersive sim. In his launch review, Phil wrote that "Prey's strengths build to create a tense and compelling atmosphere," but noted some of the tedious enemy design, most notably those bloody mimics (opens in new tab).
The game is cheap until June 1, which is when GOG's Summer Sale ends (opens in new tab). Among the usual discounts, you'll also find demos for Desperados III and the System Shock remake.