Patrick Pilmeyer, a young free software developer from Belgium, has developed Drawchemy, an Android app that allows you to doodle using your fingers and different brushes and strokes. You can also create symmetrical horizontal or vertical designs, or use both symmetries at the same time. This makes for interesting and kaleidoscopic pictures.
A similar app, which is also free software, is Webchemy. Webchemy, apart from an Android app, is also a web app, meaning that it will work from within your web browser, on any platform, be it Windows, MacOS X, Linux, Android or iOS, as long as you have a modern browser installed. Although more limited than Drawchemy, Webchemy does have the advantage that you can try it out right now.
These apps are used by professional designers to start the creative juices flowing. By doodling randomly and applying symmetry, an artist will see shapes and patterns emerge, that they can then evolve into faces, landscapes, or even mythical beasts.
Drawchemy and Webchemy are inspired by the much older software Al.chemy, a desktop application that allows for a wide variety of extensions, including really revolutionary ones, such as a plugin that allows you to “paint with sound”. You use a microphone as your paintbrush and sounds were translated to different strokes and shapes, allowing for a wild range of abstract designs. Unfortunately, Al.chemy stopped development in 2010 and no new releases appear to be forthcoming.
Drawchemy is Free and Open Source software distributed under the GPL v3 license. You can get Drawchemy from the Android Play store or you can download the source code from Google Code. Webchemy is also Free Software, has an app in the Play Store and its source code is available from GitHub.