“Participad is a WordPress plugin that allows multiple people to edit the same WP content at the same time.”
#editor
PonyEdit
Remote file editor (over SSH/SFTP) with reduced lag etc. Targeted at people who mostly work on files on remote servers.
Pixlr.com
Pretty amazing Photoshop-esque online image editor. Has most anything you “normally” use for basic image editing (including layers, cropping, selections, resize, etc etc), in a Photoshop ish package.
QuickCursor
“QuickCursor allows you to edit text from any application in your favorite text editor*.”
PDFpen
“Edit PDFs easily with PDFpen! Add text, images and signatures. Make corrections. Fill out PDF forms. Merge, delete and reorder pages.”
EtherPad
Realtime Collaborative Text Editing
EditArea
“This editor is designed to edit souce code files in a textarea. The main goal is to allow text formatting, search and replace and real-time syntax highlight (for not too heavy text).”
WordPress Plugin Readme File Generator
WordPress Plugin Readme File Generator
Simple UI which makes it easier to write a WordPress Readme.txt file (for plugins).
SQLEditor for Mac OS X
Visual editor that allows you to diagram a DB and generate the code required to actually create it.
TinyMCE Custom Buttons
Tutorial/details on how to create a plugin for the editor in WP. Add buttons, modify functionality etc.