Highlight is a "social discovery" app that notifies users when they are near someone they don't know with whom they might share interests. It runs in the background, only requiring the user's attention when it has found a potential social contact.

Andrea Vaccari, the founder of Highlight competitor Glancee, in a conference presentation that by focusing on introducing users to new people, social discovery serves as "the natural extension of social networking."

Localmind, a location-specific question-and-answer platform, offers what might be called social information. One user can find others who are currently checked in, using FourSquare, at a particular location and then ask how long the line is or which band is playing -- important questions at SXSW. Localmind launched last year at the conference and, according to co-founder and CEO Lenny Rachitsky, "is out of control" this year. Still, only 200,000 questions have been asked since the app launched, according to the company.

Localmind doesn't include advertising now, but Rachitsky said it will likely eventually look to targeted, location-based ads to generate revenue.