Or at least a very early version. From humble beginnings...
ps. Here's an early Facebook screenshot, an early Google homepage, and Yahoo's homepage circa 1994, and an early screencap of Tumblr's dashboard.
Update: If you look at the screenshot closely, there's a familiar name at the top of the "What your friends..." box: Instagram co-founder Kevin Systrom (his Twitter user id is 380...meaning that he was one of the first 400 people to sign up for the service).