Graph server

I've seen mentioned in few times sites like Digg or LinkedIn using graph servers to hold their social graphs. But the only sort of open source graph server I've found is http://neo4j.org/ .

Can anyone recommend an open source graph server?

Thanks
Aaron

Comments

[Emil Eifrem]

Out of curiousity, why don't you want to go with http://neo4j.org?

-EE

[Anonymous]

I'm not saying I would not use it, just that I already know about it. I was asking to see what other options there was.

Cheers
A