I have been playing with a module like this and I'd love to give your library a try. How can I download it? OK, found it on Github...

Cool, I added the URL to the description as well now. That one link all by itself isn't very obvious.

I'd love to incorporate this into a tACS machine, is there anymore information on this?

I'm not familiar with tACS. What's that all about?

tACS is similiar to tDCS (tACS is transcranial Alternating Current Stimulation, tDCS is transcranial Direct Current Stimulation) and it is for modulating long term potentiation in the brain. Basically, it brings the resting potential of the cells up so that it takes less stimulus for them to act (ie form a memory). DARPA even experimented with it. It was able to cut drone pilot training time in half, plus there's a multitude of other uses for it such as treatment of depression, increasing mathematical ability, focus, problem solving, memory, etc. (link here: http://www.scientificamerican.com/article/amping-up-brain-function/).

I built a simple, constant current (2mA which is what current research states should be used) tDCS machine. I've never posted any of my projects here but if you'd like I can upload the schematics, some pictures and references.

Wow. Well, I'm not familiar enough with that stuff to tell you one way or another but if you need something that will generate a low voltage sine wave between DC and 14 MHz (you can go higher but the wave get's messy) then you can pick up one of these boards off eBay for a few bucks and this library is super easy to use.