This weekend is the latest Global Game Jam, the eighth year in which developers around the globe will come together and create a game based on the theme selected for the jam -- which will be revealed at 5PM (local time, at each jam site) on Friday, when the 48-hour event commences.
If you're interested in finding out more, there's a FAQ at the GGJ site which explains things; there's also a list of participating locations which you can break down by country and metropolitan area. There are currently 636 registered GGJ sites, according to the official website.
Global Game Jam co-founder Gorm Lai recently posted about the jam's values on Gamasutra blogs, and it's worth reading if you seek a deeper understanding of the mission of the event.
"As a founder, I strongly believe that one of the stand out things about the Global Game Jam is that it is based upon a set of values; we actively promote sharing, collaboration and experimentation in game dev across the globe," Lai writes.
