Is there an open source Bitcoin exchange? I just found this project, which is described a.t.m as a learning project.

Is there a more serious, open source Bitcoin exchange? I'm aware exchanging BTC for fiat money can be quite complex, and might not fit an open source model, but an exchange specializing in crypto-currencies shouldn't be that complicated to setup, so I think there is room for an open source one.
Intersango is an open source exchange that is used at intersango.com, which is an exchange operated by The Bitcoin Consultancy. The open source project that can be found here is released under the GNU Affero General Public License. 

For more info on how to set it up, see this post on the bitcointalk forums: Intersango HOWTO - Build your own Bitcoin Exchange Web Site!