The best open source alternative to RubyMine is Atom, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to RubyMine and eight of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to RubyMine are Eclipse (Free, Open Source), Geany (Free, Open Source), Aptana Studio (Free, Open Source) and TextMate (Free, Open Source).
Aptana Studio is a complete web development environment that combines powerful authoring tools with a collection of online hosting and collaboration services that help you and your team do more. Includes support for PHP, CSS, FTP, and more...
TextMate brings Apple's approach to operating systems into the world of text editors. By bridging UNIX underpinnings and GUI, TextMate cherry-picks the best of both worlds to the benefit of expert scripters and novice users alike.
A text editor for GNOME that combines simplicity with power. Scribes focuses on streamlining your workflow. It does so by ensuring common and repetitive operations are intelligently automated. And also by eliminating factors that prevent you from focusing on your tasks.
Embitz is a free C/C++ IDE built to meet the most demanding needs of its users working in the field of embedded software development Finally, an IDE with all the features you need and operation across different targets (ARM, MSP430, PIC, ...).