An Atari 800XL. Custom OS loaded into a BASIC interpreter at startup unless you put a bootable floppy in the external 5.25" drive. We would load up DOS on the external drive and then boot whatever games my dad had pirated from his buddies. Played bootleg Ultima IV, Castle Wolfenstein (the original original one, not the 3D one) and a bunch of others. We had two cartridges (Pengo and Galaxian), but we also had 100s of games in a big shoe box of floppies.
I also learned BASIC on it at a pretty young age, which helped push me into technology as a career path, though I had to unlearn a lot of that when I got to high school and took real programming courses.
Oh good, more fucking DARVO from our conservative psychopaths.