E-Commerce and Payments category in ruby-toolbox.com
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I'm looking to setup a service that requires users to register and pay a monthly fee depending on the service selected. 

My Requirements

- Register with email and pw
- If want pro version, register with email, pw, and provide credit card info (or paypal)
  - billing occurs monthly
  - includes invoicing and payment confirmation
- Downgrade service (go back to free model)

In ruby-toolbox.com the E-Commerce and Payments category includes

1. Online Shops: Spree, RoR eCommerce, Shippinglogic, Invoicing, and Radiant Shop
2. Payments: Active Merchant, paypal_adaptive, Remit, paypal-express, Stripe, and 2 more
3. Subscription Management: Freemium, SubscriptionFu, fastspring-saasy, and subly

I'm not sure I really understand the differences between all these options. For the most part, they all sound very similar, with overlapping features. I can see which are the most popular and actively supported but between those I'm not really sure which is the best fit for my project. What am I overlooking? Which options should I consider? Is there any additional information I need to consider?