User:Danmichaelo created a neat lossless cropping tool on Tool Labs that uses OAuth so you can edit right in your browser without having a separate login.
https://commons.wikimedia.org/wiki/Commons:CropTool
OAuth consumer info: https://www.mediawiki.org/w/index.php?title=Special:OAuthListConsumers/view/...
This shows what's possible with OAuth and it'd be nice to see more such tools. There are at least a couple open source web based editors that might be fairly straightforward to integrate:
SVG-edit: http://svg-edit.googlecode.com/svn/branches/2.6/editor/svg-editor.html Microphone based recording: http://danieldemmel.me/JSSoundRecorder/
A bit more experimental (license status unclear): https://github.com/plucked/html5-audio-editor
Future (for screencast recording): https://www.webrtc-experiment.com/Pluginfree-Screen-Sharing/