Keynotopia - Prototyping straight into Keynote or Powerpoint

Justinmind - Define awesome experiences through wireframes & prototypes.

Supernotes - The fastest way to take notes and collaborate with friends. Create notecards with Markdown, LaTeX, images, emojis and more. Get started for free!

UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.

Pencil - Pencil is an animation/drawing software for Mac OS X, Windows, and Linux.

Figma - Team-based interface design, Figma lets you collaborate on designs in real time.