tk3MU is a graphical interface written in Python/Tkinter for the Roland TB303 emulator called 3MU, which can be downloaded here. 3MU originally uses a textual description of the sound and the notes to be played, and generates a sound file from this description. It works quite well..., but is not exactly user-friendly.
tk3MU is my effort to make almost all features of 3MU usable via a graphical interface. Not all features are available (this was too complicated...), but a fairly good set, including the definition of the main sound parameters and the notes to be played.