Open Source Shopping Carts

Years ago, I built an ecommerce site based on oscommerce. It worked fine. I eventually changed the platform to a WordPress plugin that was designed for me. I never was completely happy with the second format, by and large because I didn't understand it or the database structure. I would have preferred, looking back, to using Zencart or something else in a subdirectory on the site. I would have had a cohesive site this way rather than one that used the Wordpress tables as well as the plugin tables. I know there are downsides to this approach, but it allows me to more easily add my scripts and makes the site more transportable to a different platform should I decide to do that.

What are the options today for doing what I described above.