Presented here is a very basic MIDI Step Sequencer for Pure Data. It's locked to playing 16th notes, but the tempo and number of steps can be changed. The pattern can also be transposed. Finally, it comes with a decent random pattern creation system, ideal for that 'dead batteries in a 303' style sequence.
The patch itself is fairly simple; there's nothing in there a novice Pure Data-er familiar with basic messaging and lists couldn't grasp. Adding multiple pattern support would be a simple, yet interesting addition for the eager coder.
Here's a short audio demo of it at work: here, MIDI is output from Pure Data using the Mac IAC MIDI Driver (use MIDI Yoke on Windows) into Aspect, which is playing a nice analogue mono synth bass sound.
Download the patch for Pure Data here.
UPDATE: New version posted here.