Does an Open Source Trading Platform exist?
Would this be a good solution for existing/new BTC exchanges?

Some links to help you get started or make your exchange better...

Trading Platform - Exchange/market side:

• https://github.com/davout/bitcoin-central
• https://github.com/bitfloor/matching-engine
• https://github.com/dooglus/intersango
• http://www.marketcetera.com/
• Intersango HOWTO - Build your own Bitcoin Exchange Web Site! - ThiagoCMC

Trading Platform & Protocols - Order entry side:

• http://fixprotocol.org/
• http://www.interactivebrokers.com/en/software/api/api.htm
• http://www.openbloomberg.com/open-api/
• https://github.com/OpenGamma (http://www.opengamma.com/)
• http://www.nanex.net/
• http://sourceforge.net/projects/eclipsetrader/ (http://www.eclipsetrader.org/)
• http://www.traderslaboratory.com/forums/tools-trade/11086-open-source-trading-platforms-master-list.html
• http://code.google.com/p/tradelink/
• http://sourceforge.net/directory/business-enterprise/financial/investment/freshness:recently-updated/
• http://en.wikipedia.org/wiki/Category:Electronic_trading_systems

P2P Trading Platforms & Threads

• https://github.com/FellowTraveler/Open-Transactions
• https://en.bitcoin.it/wiki/Ripple_currency_exchange
• https://github.com/santacruz123/node-bitcoin-exchange
• Dark Exchange: a 100% decentralized p2p exchange - morpheus
• RFC -- Distributed Bitcoin Stock Exchange (DBSE) - btc_artist
• Open Transactions Server: Asset/Bond/Commodity/Cryptocoin/Deed/Share/Stock Exch. - markm
• P2P Cryptocoin Exchange (P2PX) - Mike3574
• P2P Exchange - "1X" and "NX", a new concept in the block - BrBoy
• p2p securities exchange. Now being developed (again) - Chaang Noi (Goat) ช้างน้อย
• [IDEA] - Ripple-like system for Bitcoin investment / p2p insurance / p2p lending - ripper234
• How and Why You Should Set Up Your Own P2P Bitcoin Currency Exchange - Trader Steve
• P2PTradeX: P2P Trading between cryptocurrencies - Sergio_Demian_Lerner