WP.osC (WP-osCommerce) is a modified version of osCommerce, one of the most popular ecommerce solutions. The main difference between WP.osC and osCommerce, is that WP.osC uses the same Theme system as WordPress.
Seems as though this is (another) fork of osCommerce. Anyway, I have been playing with this system for a couple of hours and can confirm that my own ClubosC Discount System does work with this fork (with a bit of finagling!).
As my Discount System touches very few files, it's probably the only Discount System that will work as intended with wposc, as wposc changes files considerably.
For installation of my Discount System on your wposc shop, please contact me directly on email@example.com