LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Gnoosic - Even if you don't know what you are looking for - gnod will find it.
Grammarly - Clear, effective, mistake-free writing everywhere you type.
Musicroamer - A visual Pandora for discovering new music
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.
Songstack - Swipe to discover new music for Spotify