A very interesting texture generator written in Java. The program has an brush/bristle creation tool that makes complex pattern creation easy.
The program is very fun to play with. The concept is designing brushes utilizing 2D vector shapes as bristles for the brush. A single brush can have many different layers of bristles. And each bristle can have alphas, blend settings (screen, multiply, etc.). And while you paint you can set things up so the resulting image is tileable by wrapping the brush strokes around. I'd recommend if you download it to work through the tutorials for a little rundown on how everything works. The idea is something I haven't seen before and allows for a high level of detail in a brush that you normally wouldn't see. Its easy to get some fairly nice effects that give textures a pitted, dirty, or withered, or aged look. It's also good for producing surfaces like rock, repeating patterns like tiles, etc.
The author Jim Heffner says:
Semicuro is a Java-based application designed to facilitate the creation of complex bitmapped textures. Aged wood, hard surfaces like rock or concrete, textures that require subtle variations in color and/or "feel", are particularly good targets, but there are few limits on what can be produced.
Semicuro's unique quality it its "one brush, many bristles" approach to painting. Rather than a linearly-defined set of attributes for a single brush(which is typical of most paint apps), Semicuro allows you to define any number of bristles for each brush. Each bristle is essentially a brush unto itself, each with its own settings. When all these bristles are painted at once, the results can be quite interesting.
Creating bristles is easy - just use any of the five drawing tools to draw its shape, and then change the various attributes to suit your needs. There's a lot of room for experimentation, so have fun!
Semicuro is open source; visit their website for downloads and tutorials.