Rapid applications development tool and libraries for FPC
The Lazarus IDE is a stable and feature rich visual programming environment for the FreePascal Compiler. It supports the creation of self-standing graphical and console applications and runs on Linux, FreeBSD, MacOSX and Windows.
A free IDE for C#, VB.NET, & Boo projects on Microsoft's .NET platform
SharpDevelop is the open-source IDE for the .NET platform. Write applications in languages including C#, VB.NET, F#, IronPython and IronRuby, as well as target rich and reach: Windows Forms or WPF, as well as ASP.NET MVC and WCF. It starts from USB drives, supports read-only projects, comes with integrated unit and performance testing tools, Git, NuGet and a lot more features that make you productive as a developer.
An open-source x64/x32 debugger for windows.
An open-source x64/x32 debugger for windows. Development is done on GitHub (https://github.com/x64dbg/x64dbg). Daily snapshots are uploaded here, snapshots for every commit can be found on http://releases.x64dbg.com
Edyuk is a free, open source, fast and lightweight development environment which supports C++ and Qt 4 out of the box and can be extended through plugins. It works under all platforms supported by Qt 4 (Linux, Mac, Windows, BSD, ...).
GPL task manager replacement for Windows
Daphne is a system tray application for process killing, controlling and debugging. It's development started back in 2005. It was first thought to kill a set of windows process at once. With the time it became a GPL task manager replacement for Windows. You can kill a process by dragging the mouse over the windows, by right-clicking the process in the main process list, or by typing its name with the "Kill all by name" command. You can set a any window to be always on top, to be transparent, to be enable, et cetera. Although Daphne was born just to kill windows process. You can think of Daphne as a task manager replacement. The main window displays a list of currently running process with detailed information about: CPU usage, Process ID, Process name, Full path (and arguments), Priority, Class (Process / Service), Current memory usage, Peek memory usage, Current swap usage, Peek swap usage and Number of threads.