I couldn't find an open-source inventory management system I liked, so I started working on one. It was designed to handle multiple stores, each with their own inventory and products. Each product in categories and sub-categories, and location management for each item. It was supposed to be the base of a few online stores and a brick and mortar shop, but that business plan fell through. Still working on the inventory system, and it still needs more work.

https://github.com/SeleneSoftware/inventory