LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Songstack - Swipe to discover new music for Spotify
Grammarly - Clear, effective, mistake-free writing everywhere you type.
Music Walker - Explore and play (via YouTube) songs similar to a seed song.
Gramlee.com - Online grammar check, proofreading and copy editing services.
Gnoosic - Even if you don't know what you are looking for - gnod will find it.