As someone reaching 50 years old, we always had such indies, we used to call them bedroom coders, and distributions came in tapes, floppies in magazine covers, shareware CD-ROM and DVD-ROMs.

Maybe it only got visible to the consoles generation around the time of XBLA arcade, and even that was already predated by PS Yaroze and PS2Linux efforts.

Before Unity, we had SDL, Ogre3D, SFML,... but naturally all of those require more coding skills than engines designed with UI workflows in mind.