If you're a huge fan of abstract wallpaper but you don't have the software or the know-how to make one you'll definitely want to try Flame, a web-based drawing tool that makes creating abstract doodles easy and fun.
Using Flame you can create a variety of shapes and patterns and the user interface is simple. You have a palette which is black by default, white is the only other option. You have an adjustable brush, customisable in size, softness and other variables, and you can select your colours and the level of opacity and saturation.
One of the best ways to create really soft and flowing lines is to move the mouse quickly. The faster you move the mouse the "wider" the brush stretches and the softer and more diffuse the lines are. If you move the mouse slowly you get a laser-focused beam of intense colour, move it quickly and you get a wide swath of gossamer-like colour.
You can save your pictures to your computer, the default size is 1680px × 1050px with no ability to select other sizes — a feature we'd love to see implemented for creating crazy triple-screen wallpaper and other sizes.