Descent is a series of shooters known for its full freedom of movement in all three dimensions. The source code for the first two games in the series has been freely available since the late 1990s.
Descent 4 has been in and out of development several times in the decade since the release of Descent 3. Since 2009, Interplay is considering bringing the series back, due to announcements that they would focus on exploiting some of their existing intellectual property, including Descent. Two projects started on Kickstarter, both involving staff from the original series, and both games will be released in 2018 (Descent: Underground and Overload).