Facepunch Studios is hard at work developing a spiritual Garry's Mod successor that they're calling s&box. The sandbox style game started life out as an Unreal Engine project but has since swapped to using Source 2, the engine developed by Valve that is currently in use in games like Dota 2 and Half-Life: Alyx.
Thanks to the limited public availability of s&box to eager developers, Source 2 is...