Anjuta
Develop software in an integrated development environment

Ninja IDE
A Python IDE

Code::Blocks IDE
Configurable and extensible IDE

CoqIDE Proof Assistant
Graphical interface for the Coq proof assistant

Eclipse
Eclipse Integrated Development Environment

Eric python IDE
Integrated Development Environment for Python
Frama-C
Framework for source code analysis of software written in C
Geany
A fast and lightweight IDE using GTK+
gPHPEdit
Edit PHP source files
Lazarus (1.4.0)
Lazarus IDE (1.4.0)
Plasmoidviewer
Testing tool for Plasma applets

Monkey Studio IDE
The best cross platform IDE available!
MonoDevelop
Develop .NET applications in an Integrated Development Environment

NetBeans
Integrated Development Environment
OpenSesame
Graphical experiment builder for the social sciences
PIDA
Python Integrated Development Application
Cuttlefish
List and preview available icons
ProjectCenter
The Official GNUstep IDE

Proof General
Organise your proofs!

Pyragua
A fast and lightweight IDE using wxPython

QDevelop
A development environment dedicated to Qt4

SLUDGE Floor Maker
Edit SLUDGE floor plans

SLUDGE Project Manager
Manage and compile SLUDGE projects

SLUDGE Sprite Bank Editor
Edit SLUDGE sprite banks

SLUDGE Translation Editor
Edit SLUDGE translation files

SLUDGE Z-Buffer Maker
Edit SLUDGE z-buffer files

SPE (Stani's Python Editor)
Integrated Python Development Environment

Spyder3
The Scientific Python Development Environment - Python 3

Spyder
The Scientific Python Development Environment
Lazarus (1.8.4)
Lazarus IDE (1.8.4)

Thonny
Python IDE for beginners

Arduino IDE
Open-source electronics prototyping platform

eric6
Integrated Development Environment for Python
Fritzing
Electronic Design Automation software
GNAT Programming Studio
Integrated Development Environment

Builder
Build software for GNOME

KDevelop
Plugin-extensible IDE for C/C++ and other programming languages

KDevelop (Pick Session)
Plugin-extensible IDE for C/C++ and other programming languages (Pick Session to start with)
Lazarus
Lazarus IDE
Lazarus (1.6.2)
Lazarus IDE (1.6.2)
Lazarus (1.6)
Lazarus IDE (1.6)