Google Talk client in the form of a Chrome extension. Pressing a hotkey (default to ctrl+d) brings up a lightbox-style chat window regardless of which tab you're on.
Since chats can be opened on any tabs, some context-sensitive features are added, such as shortcut to send the current URL over IM.
Some other features such as image previews are also present.
Multi-user, synchronous photo editing experience using Aviary web widget. Think of it as if Aviary and Google Docs had a beautiful baby together.
Get help from people that are already there to do things for you.
Droptask is a platform for asking for help at a particular place, from people who are already checked in there. With Droptask, you can avoid standing in lines by asking someone to hold your spot, or check in on whether a bar is too crowded by setting up a task for people who are already there.
It works on a credit system at present, where you reward others who complete your task with credits, and earn credits by taking tasks from others!
Eventually, the credit system can be replaced with real financial transactions and Foursquare users will be able to earn money even as they wait in line.
Chrome extension that unleashes the graffiti artist in all of us.