A very advanced platform suitable for various forms of development.
Gliffy diagram editor
Gliffy is a free and easy to use diagram editor with export to png graphics and more. It can be run as a Chrome app.
yED graphic editor
yED is a good and free diagram editor with advanced features like auto-reordering. There is even an online version.
Notepad++ source editor
A great and free sourcecode editor. Can be expanded with several plugins. With the ftp plugin very suited for hardcoding websites!