Every day, hundreds of millions of us go to Facebook or Flickr or YouTube to see what our friends are up to, to look at photos or videos, and to meet new people. And no doubt a 3D virtual world would make all those things more fun. But the reality is that while social networks have exploded in growth, virtual worlds like Second Life have stagnated, as have Vivaty.com and Google’s Lively. JustLeapIn.com aims to change all that. JustLeapIn.com offers a browser-based application with no additional plug-in required to join. JustLeapIn is kind of like The Sims meets social networking: you can share photos, add music, and meet new people.