atomswarm

atomswarm is

"a framework for performance and composition, based on swarming behaviours similar to those seen in flocks of social animals. It can be thought of as a self-organising ecosystem, whose structure is internally regulated by limited resource availability and each agent's pursuit of internal homeostasis.

Sonic behaviours are determined by each agent's genetic disposition, the relationships between agents, and the population's continued evolution over time."

I saw a performance/demo of this software at a conference and was impressed. Whilst it can sometimes be hard to associate the onscreen movements with the generated sound, the majority of the time things do make sense. The output of the system looks and sounds very impressive.
At the website you can find links to video and audio as well as a description of the project along with examples of the code used.
The site also contains info on the developers other projects

free generative sequencer (mac only)

nodal is a free (for non-commercial use) app for developing generative musical systems and transmitting MIDI.

"Nodal is a generative software application for composing music. It uses a novel method for the notation and playing of MIDI based music. This method is based around the concept of a user-defined graph. The graph consists of nodes (musical events) and edges (connections between events). You interactively define the graph, which is then traversed by any number of players who play the musical events as they encounter them on the graph. The time taken to travel from one node to another is based on the length of the edges that connect the nodes."

As Nodal outputs MIDI data it would be interesting to use in conjunction with programs like MaxMSP or pd. You could also use it to control sequencers/DAWs either in the studio or out live.

The Nodal website has a binch of tutorials and examples for you to dig around in.