Frenzy vs Spree: What are the differences?

Developers describe Frenzy as "Sell to the most loyal customers in a new way (by Shopify)". Frenzy is built on Shopify’s highly scalable platform so you can sleep easy knowing your customers will always have a fast, enjoyable experience. Whether it’s a big flash sale, Black Friday or just the normal high order volume of your successful store, we want your business to succeed. On the other hand, Spree is detailed as "A complete open source ecommerce solution for Ruby on Rails". The Spree storefront offers a full feature set and is built on common standards, so you don't have to compromise speed to market, efficiency or innovation. The modular platform allows you to easily configure, supplement or replace any functionality you need, so that you can build the exact storefront that you want.

Frenzy and Spree can be primarily classified as "Ecommerce" tools.

Spree is an open source tool with 9.83K GitHub stars and 4.32K GitHub forks. Here's a link to Spree's open source repository on GitHub.