Two things you'll notice about Seth Priebatsch: One, his infectious, get-you-out-of-your-chair enthusiasm. Two, the inventory of entrepreneurial feats he's managed to accumulate at a remarkably young age. The 21-year-old founded his first startup at age 12, and by age 18, he'd founded another -- PostcardTech, which makes interactive marketing tours for CD-ROM.

Now he's working on SCVNGR, "a massive experiment in building a mobile game together." Backed by Google Ventures, SCVNGR is part game, part game platform. Players play SCVNGR by going places, doing challenges and having fun -- outside of the office, beyond the screen, in the real world. Organizations use SCVNGR by building on the game layer by adding their own challenges to the places they care about.