This is a simple example I built while playing with Sinatra and Cucumber a bit, so that I could get to a good starting point.

Social Stream is a Ruby on Rails engine providing your application with social networking features and activity streams. This gem packages the basic functionality, along with basic actors (user, group) and activity objects (post and comments)

Adyen HPP payments for Solidus Stores

Enhanced SEO in Solidus

Overview dashboard for use with Solidus.

This incomplete but very satisfying list of devices, will help you run your app on so many devices!

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Special Delivery is a Rails engine that enables powerful and easy-to-use callbacks in response to Mailgun events POSTed via webhook.

Splinter is a Capybara Ninja

Spree's Authenticattion API

Add comfortable mexican sofa CMS to spree commerce

Crux enables creation of separate On-Line store for paid registered users.

Display Custom notifications on Spree Store

Spree Developer Tools

With this gem you get an faq page and the management tools to make it very easy to update your faq and reduce the demand on your sites customer service

Allow Spree to upload multi product images at the same time

Liqpay.com payment gateway integration for Spree E-Commerce.

it uses the standard method like spree_i18n

As spree doesn't update line items price when products price changes, this extension do it.

Add support for Pagseguro checkout as a payment method.