[Update 3/4/17 Looks like Shawn pulled the tDCS pages from his website. Though it’s still available via WebArchive. But the GitHub link is good.] A DIY tDCS project from Shawn Nock [Update 8/12/12 Shawn has updated his project to derive power via USB!]
Practically speaking, this means that anyone interested in tdcs may (at their own risk): Download the designs, edit or modify them, fork their own design, and sell a product based on this design all without any proprietary (expensive) software.
Those who aren’t inclined to make changes, but want to experiment, can use the pcb design and the bill of materials to make small batches of devices for testing or personal use.