Phoenix is a modern open-source Code Editor for the web
Apache NetBeans
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A web based file manager, web IDE / browser based code editor
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Modernized fork of NEdit, with unicode support and AA text rendering
A hackable text editor for the 21st Century
Web IDE in single HTML file
IDLE Extensions
Open Source C & C++ IDE for Windows
Launch an external diff tool like WinMerge in Eclipse
A modern, lightweight yet powerful text editor
A lightweight programming environment for Java