Evolvotron is an interactive "generative art" application to evolve images/textures/patterns through an iterative process of random mutation and user-selection driven evolution. If you like lava lamps, and never got tired of the Mandelbrot set, this could be the software for you. It's implemented using Qt, and is multithreaded.
ucanvcam is a cross-platform framework for building virtual cameras. Virtual cameras offer the same interface as regular cameras to client applications (such as Skype), but provide user-generated or user-modified imagery rather than imagery directly from a camera. While ucanvcam comes with a set of special effects, the main intent is to make building virtual cameras easier for people without OS-specific knowledge, so they can focus purely on image processing.
AZR3-JACK is a port of the free VST plugin AZR-3. It is a tonewheel organ with drawbars, distortion and rotating speakers. The original was written by Rumpelrausch Täips. The organ has three sections, two polyphonic with 9 drawbars each and one monophonic bass section with 5 drawbars. The two polyphonic sections respond to events on MIDI channel 1 and 2, and an optional keyboard split function makes the bass section listen to the lower keys on channel 1. The three sections have separate sustain and percussion switches as well as separate volume controls, and the two polyphonic sections have separate vibrato settings. All three sections are mixed and sent through the distortion effect and the rotating speakers simulator, where the modulation wheel can be used to switch between fast and slow rotation, and the fast and slow rotation speeds themselves can be changed separately for the lower and upper frequencies.
Flowpaint is a next generation paint program that focuses on usability and power. It's cross platform and supports pressure sensitive graphics tablets. Planned features for future versions include user-editable procedural brushes, brushes created from pictures, layers with arbitrary data channels, infinite and wrapping canvas layouts, parametrized picture templates, and built-in support for downloading and sharing new brushes and templates.
Grafx2 is a bitmap paint program that allows you to draw in more than 60 video resolutions (from 320x200 to 1024x768, including most of the standard Amiga resolutions: 320x256, 320x512, 640x256, 640x512, and more, provided your video card knows how to handle them). Its layout is not very different from the famous Deluxe Paint or Brilliance, so it will be quite easy to handle it if you know at least one of these programs.