VST recommendation for specifying frequencies

[driven]

I've got an itch to play with experimental music (think deep house, but different tones and time signatures) where I need to control the frequency of the synth to the hertz. Operator does it, but it's a bit boring. I've never played with VSTs before, so this will be a first.

Looking for a recommendation for a fairly low CPU (2.5GHz i5Macbook Pro) VST that'll do this fine frequency control -- or custom scales would also work. Free is great, but I don't mind spending up to $100. Ideas?

[siliconarc]

Madrona Labs Aalto

[driven]

Madrona Labs Aalto

That looks killer. Even takes Scala files if I want to play with weird scales.

Found a review video here: https://www.youtube.com/watch?v=XHPFqIYEE8U

Downloading the free demo: http://madronalabs.com/products/aalto

Here goes nuthin!