user78: 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.

user1162: Try this Chinese opensource project http://www.peat.io/
They've released their source code under the MIT License, and claim to have a fully functional platform.

user3795: The bitcoin-central.net exchange claims to be open as well, but they are currently(as of March 2nd 2013) "down for maintenance". The code can be found at github and bitcoin-central is part of the paymium payment network.
The network, including bitcoin-central, is somewhat backed by the french taxpayer:

The ﬁrst ﬁnancially registered Bitcoin exchange,
  bitcoin‑central.net is the leading European exchange running without
  disruption since January 2011.
Customer deposits in Euros are held separately by Aqoba, licensed as a
  payment institution by Banque of France. A debit card will be offered
  soon to veriﬁed account holders.


user659: The code that Intersango runs is no longer open source as I understand it.
The Australian World Bitcoin Exchange uses a heavily modified version of the old open source Intersango code, and remains open source.
Full disclosure: I'm the one who heavily modified it.  :)
Fiat deposits and withdrawals are handled manually.  For a while we looked into automating the process, but the bank charges more for the necessary banking API than the  exchange generates in commission.

user105: 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!

78: <p>I just found <a href="https://github.com/enmaku/btc_exchange">this project</a>, which is described a.t.m as a learning project.</p>

<p>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.</p>
 1162: <p>Try this Chinese opensource project <a href="http://www.peat.io/" rel="nofollow">http://www.peat.io/</a></p>

<p>They've released their source code under the MIT License, and claim to have a fully functional platform.</p>
 3795: <p>The bitcoin-central.net exchange claims to be open as well, but they are currently(as of March 2nd 2013) "down for maintenance". The code can be found at <a href="https://github.com/davout/bitcoin-central" rel="nofollow">github</a> and bitcoin-central is part of the <a href="http://paymium.com/" rel="nofollow">paymium</a> payment network.</p>

<p>The network, including bitcoin-central, is somewhat backed by the french taxpayer:</p>

<blockquote>
  <p>The ﬁrst ﬁnancially registered Bitcoin exchange,
  bitcoin‑central.net is the leading European exchange running without
  disruption since January 2011.</p>
  
  <p>Customer deposits in Euros are held separately by Aqoba, licensed as a
  payment institution by Banque of France. A debit card will be offered
  soon to veriﬁed account holders.</p>
</blockquote>
 659: <p>The code that <a href="https://intersango.com/">Intersango</a> runs is no longer open source as I understand it.</p>

<p>The Australian <a href="https://www.worldbitcoinexchange.com/">World Bitcoin Exchange</a> uses a <a href="https://github.com/dooglus/intersango/commits/aud">heavily modified</a> version of the old open source Intersango code, and remains open source.</p>

<p>Full disclosure: I'm the one who heavily modified it.  :)</p>

<p>Fiat deposits and withdrawals are handled manually.  For a while we looked into automating the process, but the bank charges more for the necessary <a href="http://www.xero.com/">banking API</a> than the  exchange generates in commission.</p>
 105: <p>Intersango is an open source exchange that is used at <a href="http://www.intersango.com">intersango.com</a>, which is an exchange operated by <a href="https://bitcoinconsultancy.com/">The Bitcoin Consultancy</a>. The open source project that can be found <a href="http://gitorious.org/intersango">here</a> is released under the <a href="http://www.gnu.org/licenses/agpl.html">GNU Affero General Public License</a>. </p>

<p>For more info on how to set it up, see this post on the bitcointalk forums: <a href="https://bitcointalk.org/index.php?topic=35812.0">Intersango HOWTO - Build your own Bitcoin Exchange Web Site!</a></p>
