In a blog post on Amplitude Studios' blog, it has been announced that special, in-game items will be available until January 25. All you've got to do is log on and play any of the games in the Endless franchise: Dungeon of the Endless, Endless Space or Endless Legend.
This event is to commemorate Amplitude Studios' forming. They write:
On a cold day of January 21st 2011, the paperwork for a new company called AMPLITUDE Studios (note the plural as we were already expecting to operate 27 different studios) was recorded at the local registration office. We quickly snagged some offices, hijacked our friends and family for some money, hired talented people that still constitute the core of Amplitude today, and started working on our first game.
After some more history is divulged, the studio announced that commemorative items would be available for just a few days.
Anyway, this anniversary has given us the idea to celebrate an Endless Day. Rumor has it that this event could occur on a yearly basis. Be prepared for in-game events, rewards, gifts and whatnot. Also for those in Paris on the 21st, we are hosting a Beer2Gether at our offices.
Make sure to get in while you can! These sort of events will slip past you very quickly if you're not careful.