Questler is a web experience that focuses on informal learning from friends, peers and experts outside formal learning institutions. Having said that the Quest tool does seem to intersect with Yahoo!Answers and LinkedIn Answers yet the focus here is the Quest it self in starting conversations that seek different point of views rather than getting right-on answers.

The current toolset which includes Quests and Discoveries; will be expanded in the near future to have other tools that will help cultivate and capture informal learning...its in the oven!

I haven't taken a look at twibrains but will do very soon!