I'm working on the concept for a new drawing app called Hexel Art. It's just like pixel art, but with hexagons, arranged on a 100x100 rectangular grid. (See Red Blob Games for info on hexagonal grids). The app has a brush tool, a paint bucket tool, and tools for drawing lines and basic shapes (using techniques from my Drawing shapes based on user input post). The app also allows you to upload an image onto the grid and draw over it. When you're done drawing, either right click the canvas and save it as an image, or click the 'Download' button to save your art as a 100x100 .png file that you can later reupload and modify.
A prototype for the app is below - please test it out and give me your suggestions! Note: Prototype uses WebGL, which may not display on mobile devices or old web browsers.