procedural shapes for Unity UI
create and edit UI directly in the editor, without the need for textures
UI Shapes Kit is available under the MIT License. This means that you can use it in any commercial or noncommercial project. The only requirement is that you need to include attribution in your game's docs. A credit would be very, very nice, too, but isn't required. If you'd like to know more about what this license lets you do tldrlegal.com have a very nice write up about the MIT license that you might find useful.
UI Shapes Kit was originally created by this other thing