Doka.Photo - Edit images without leaving your browser
Smartmockups - Create stunning product mockups, easily and online.
Sumo Paint - Photoshop in your browser, Sumo Paint an advanced browser-based image editor.
AppLaunchpad - Create free beautiful screenshots for App store/Google play
Really Good UX - A library of screenshots for UX inspiration
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.