Hex is a free multi-track MIDI sequencer that facilitates music composition in microtonal tunings. It integrates seamlessly with the DT-enabled synthesizers, or with any standard MIDI synthesizer. Moreover, it can also be used in conjunction with a digital audio workstation such as Pro Tools, Logic, Steinberg Cubase, Cockos Reaper, Ableton Live, Tracktion or Cakewalk SONAR.
The Viking is a free software synthesizer available as a standalone application. It is portable, requiring no installation. Simply unzip the .zip file and run the executable inside.