The name "Blizzard" doesn't tend to make one think of 16-bit platformers, but in the mid-90s that's exactly what they made. Blackthorne certainly isn't what you expect from the developer more known for hardcore PC genres like MMOs and RTS, but Blizzard is acknowledging its youthful experimentation by releasing it for free.
Blackthorne has you play as Kyle, a shotgun-wielding 90s stereotype seeking revenge. It saw its share of ports throughout the 90s to various game consoles, but Blizzard last acknowledged it in 2010 with a cheeky April Fool's gag. If you have a Battle.net account you can pick it up now for free, as reported by Joystiq. Once you've downloaded it, it will stay in your library for keeps. This only goes for US accounts, apparently, so those of you pining for nostalgia in other countries are out of luck.