Giada is a free sequencer environment for handling your samples and loops. VSTs can be loaded as well. Here´s a demo vid:
The Music and Sound Design Platform (also referred to as Music_SDP and MSDP) is free and open-source software built for electronic and electroacoustic music performance, production, improvisation, and experimentation. Music_SDP is a DAPE, or Digital Audio Performance Environment, functioning similarly to a DAW (Digital Audio Workstation), but designed with a special modular structure built for live performances. MSDP provides a non-linear, infinitely expandable, totally hackable, easy-to-use interface for sound design that encourages and rewards exploration and experimentation. It is a great platform for beginners and professionals alike, and provides all the tooling and control needed to make wild new sounds, build complex sonic projects, and execute flawless performances.
RandARP is a free VST plugin arpeggiator with many randomization features, allowing incoming notes or chords to be manipulated in various rhythmic ways.
Random Riff Generator is a midi tool by Mario Nieto that generates sequences for you. This is the free version.
This is crazy. Loligo is an experimental audio tool that generates sound from image data. Watch the vid and download here.