An exhaustive list would be a bit much to come up with on the spur of the moment. I thought a Sega Megadrive/Genesis would be the most likely system recognised by most 14yr olds :-) But off the top of my head, I know the 68000 was in:
-NeoGeo @ 12mhz.
-Multitudes of those 2d arcade games (often accompanied by a z80 for sound and numerous house-keeping activities. I've looked in MAME too ;-)
-Amiga 500/600 @ 7.6 mhz
-Mac Classic (@ 8 mhz?)
-Low-power versions at speeds of up to 32mhz were in various PDAs up until a few years ago
-Megadrive/Genesis.
-It was in the Sega Saturn as a sound processor
-In the Jaguar for house-keeping.