Artboard Studio - Online graphic design app mainly focused on product mockups.
Now UI Kit - A beautiful Bootstrap 4 UI kit. Yours free.
Vectr - Free vector graphics editor. A simple yet powerful web and desktop cross-platform tool for everyone.
Bots UI Kit - Fully customizable Sketch UI Kit for Messenger Platform
Canva - Canva is a graphic-design platform with a drag-and-drop interface to create print or visual content while providing templates, images, and fonts. Canva makes graphic design more straightforward and accessible regardless of skill level.
Landing UI Kit - Handcrafted UI components for landing pages