Probe is created by Synoptic, a relatively large company in this field who also makes Virtual Waves, one of the first software synthesizers (though not realtime). Each voice in Probe has 3 oscillators and 2 filters. As well as the standard waveforms, 20 harmonic additive synthesis and live audio input are also available. High and low pass filters are available at 6, 12, 18 and 24db/Oct. The only way to get a band pass effect is to use both a high pass and a low pass filter. There are 2 LFOs with the unusual feature of being able to use a live input envelope. A modulation matrix is available.
A pattern based sequencer is available which can also be used to trigger WAV files for drums - some are provided. Synthesis paramteres can be directly edited from the sequencer. Echo, reverb and distortion are provided on the output stage, and a DirectX plugin can also be added. While the specification is quite competent with a few features not commonly seen, the output doesn't distinguish itself from programs at a lower price point. The website makes claims about how it can "reproduce sounds from the legendary vintage machines (Bassline, Minimoog, Prophet V etc…)" - but it doesn't do this any better than the next soft synth.
Probe SE is similar to Probe, however it only supports 4 voices instead of 16 and doesn't have the sequencer. The support for DirectX plugins is also removed. Probe costs $199 while Probe SE costs $69, both of which seem a bit excessive for what is provided.