Eric is a full featured Python and Ruby editor and IDE, written in python. It is based on the cross platform Qt gui toolkit, integrating the highly flexible Scintilla editor control.
Ultimate++ is a C++ cross-platform rapid application development suite focused on programmers productivity. It includes a set of libraries (GUI, SQL, etc..), and an integrated development environment.
All the tools software developers need to create cross-platform Java desktop, enterprise and web applications. Runs on Windows, Linux, MacOS, as well as Solaris. It is easy to install and use, works right out of the box -- and it is open-source and free!
Eclipse is an open source community whose projects are focused on building an open development platform comprised of extensible frameworks, tools and runtimes for building, deploying and managing software across the lifecycle. A large and vibrant ecosystem of major technology vendors, innovative start-ups, universities, research institutions and individuals extend, complement and support the Eclipse platform.