AudioRealism has released Universal Binary AU versions of Bass Line and Bass Line Pro for Mac OS X.

The downloads function as demo versions if you don't own a license.

In My Dream App, a competition between different applications ideas submitted by aspiring apps designers, one of the final 18 contestants is Whistler. Whistler is a software that translates your humming, whistling or tapping, into melodies and beats. In addition it is able to load plugins and letting you dress and layer your inputted whistling and tapping in instruments and arrangments.
The winning app design will be coded and put on the market, so if it sounds good, get voting!

Inspired by classic hardware - Latronic Nortron - DSP Audio has released Nortron 1.0, a virtual step sequencer which can control Softsynths and standard MIDI devices through IAC and CoreMIDI.
Nortron is Mac OSX 10.2, 10.3 Panther and Tiger compatible and is available for $200 USD.
More details on DSP Audio website.

D16 group has released a Mac version of Phoscyon, their TB-303 emulation. At this time Mac version is available in Universal Binary format as VSTi plugin (Audio Units to follow).

For more info about Phoscyon visit the d16 group website.

MHC announces Industrial Tones 1.0, a synthesizer which plays an extensive set of industrial waveforms, processing these using a filter, envelopes, an LFO, an ensemble, delays and an effect section which features 133 different effect modes, including their "unique crossfading effects and layered effects".
Version 1.0 has been released as a VSTi for Windows and an AudioUnit version for Mac OS X (Universal Binary) will soon be available.

More details on MHC website.