Started as 20% project from a Google employee.

http://en.wikipedia.org/wiki/Orkut_B%C3%BCy%C3%BCkk%C3%B6kte...

Perhaps it depends on too much of the internal infrastructure they wouldn't want to sell?

Legally, it was created at Google. Technically, Orkut software was copied from the startup that Orkut the person was hired from.

They should open source it.

It probably would take too much effort to make it usable without Google's internal APIs (storage, search, etc).

They could open source it and have other people use app engine if people want to use it. Otherwise if its open source people could implement what ever they want on the back end.

App Engine is very different from the internal APIs most production services depend on.

It says in the second sentence of the announcement that it was a "20 percent project" - basically, it was started by one or more Google engineers as a side project and developed into a full-fledged attempt to create a Google-based social networking site.

I think it was one of their engineer's 20% time project. I haven't logged into orkut in 6 years so I don't recall. I'm sure wikipedia has info on it.

You are correct, it's even named after the engineer that started it.