Sega is celebrating its 60th anniversary this year and it's marking the occasion with a week of festivities on Steam. There's a sale on many Sega games including Persona 4 Golden, Bayonetta and the Total War series. You can claim a couple of titles for free, including Sonic The Hedgehog 2 (the best Sonic game, IMO).
To snag the classic Saturn title NiGHTS Into Dreams gratis, you'll need to link your Steam account to your email address at a site Sega set up by December 13th. You'll also receive "exclusive access to weekly goodies drops" over the next several weeks.