CodeLite is an open source, free, cross platform IDE specialized in C, C++, PHP and JavaScript, which runs best on all major Platforms such as Windows, MacOS or Linux.
It's the only IDE that has C++ code completion and refactoring that isn't as slow as in Eclipse. I also like it comes with Ruby support which I use daily.
The program is limited in what it can do with certain features, such as end-user coding and different languages. But for basic needs, this software is the best on the market that I have found.
The GUI debugger does not expose advanced features of gdb. Workaround: it is possible to execute gdb commands directly.