While searching for my life-long dream of developing a trading platform, I found these to be fully matured. All are Java based.
- Eclipse Trader is an Eclipse Rich Client Platform (RCP) application focused to the building of an online stock trading system.
- Humai Trader Platform is a free, open source stock technical analysis platform built on pure java. The project was renamed to Blogtrader.
- jrobotrader is a simulation platform for automated stock exchange trading.
- ActiveQuant open source java trading libraries and the former version ccapi2.
- TA-Lib: Technical Analysis Library is now also available as a pure java library.
- Rmetrics Software for Financial Engineering and Computational Finance (not Java!).
- Open Java Trading Platform is meant to be a common infrastructure to develop stock trading systems.