Invision - Prototyping and collaboration for design teams
Grammarly - Clear, effective, mistake-free writing everywhere you type.
Proto.io - Create fully-interactive high-fidelity prototypes in minutes that look and work exactly like your app should. Sign up for a free 15-day trial and get started.
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Zeplin - Collaboration app for UI designers & frontend developers
ProWritingAid - For the smarter writer. A grammar checker, style editor, and writing mentor in one package.