Google Glass is still in its infancy, but it's clearly gaining traction. The $1,500 wearable computer became available for purchase again May 13 after selling out in one day during its initial public sale last month. Developers, meanwhile, are cranking out apps to make the hands-free headset more useful. OpenTable, Foursquare, and TripIt are the newest Glass apps, also known as Glassware, joining existing ones from Twitter, Facebook, and others. Several apps are also in development that make Glass more relevant for meetings and events. Here are five to keep on your radar.