Dev - Also, on form submission, use GD to resize the image as a new thumbnail file
Dev - In the submission form, you can now upload a banner image
This is more of a prototype for what I envision this project to become, so configuration is still minimal. Eventually it will support rendering to disk, loop points, and a modular editor / custom file format, but this is all still in the works. For now, you're stuck writing the shaders by hand, but that doesn't mean they're any less fun to tweak ;)
If you don't know where to start, just look through the included shaders and poke around. Change some contants, replace cos with tan, take the square root, whatever your heart desires. If you don't know GLSL, fear not. When you think you've got the jist of it, start writing your own from scratch! And feel free to post it in the comments here. I'd love to see what others can come up with.
Oh, and if you have any suggestions for features to add, post them as well. Same with bugs, though I hope no one comes across any in normal operation.
Edit: Minor update. Cleaned up some of the included shaders, and added a modified Programmer's Notepad (portable) that supports GLSL syntax highlighting / keyword completion (so you have a better default editor than notepad).
Also, I'm working on refactoring the code, which will be made available on Github when I can get it to a more organized state.