The porting story goes back to 2009, when id Software brought official versions of Wolfenstein 3D and the original Doom to the iOS App Store. Updates for those ports stopped in 2014, though, and that became a problem in 2017, when iOS 10.3 officially stopped supporting “legacy” apps developed with a deprecated 32-bit codebase.

That sunsetting inspired mobile developer Tom Kidd, who noted that both Wolfenstein 3D and Doom had long been available as open source apps on id Software’s GitHub page, complete with the iOS versions of their respective engines. “I went and did the work to update them and get them working in the latest versions of iOS,” Kidd wrote last year. “This wound up being both harder and easier than I expected.”