Developer id Software once made a PC port of Super Mario Bros 3. which Nintendo declined to produce, but led to the development of Commander Keen.
Studio founder John Romero shared footage of the port on Twitter in honour of Commander Keen’s 25th anniversary.
Happy 25th Birthday, Commander Keen! In honor I'm sharing a video of our SMB3 demo we made for Nintendo on 9/28/1990.https://t.co/R2GlSYCoBM
— 𝕵𝖔𝖍𝖓 𝕽𝖔𝖒𝖊𝖗𝖔 (@romero) December 14, 2015
The studio is currently developing Doom for Bethesda.