[jonah]

If you're not tied to PHP, check out Spree[1] or its fork Solidus[2].

[1] https://spreecommerce.com/ [2] http://solidus.io/

[hardwaresofton]

Why are they both built on rails?

I'm a little intimidated by the fact that if I have a problem with my store front, and start to look under the covers to fix things, I'd be hit with the full complexity of entering a new rails codebase.