Kdevelop is a free IDE for KDE that uses external compilers like gcc. It includes features like a source code editor with syntax highlighting and automatic indentation, project management, a GUI designer, and automatic code completion for C/C++. Eclipse is primarily for Java development but has plugins for other languages like C/C++. MonoDevelop is for C# and .NET development on GNOME, and includes features like code completion and class management. MATLAB is a numerical computing environment but requires cracking to use for free.