Splitwise - Splitwise is a free tool for friends and roommates to track bills and other shared expenses, so that everyone gets paid back. On the web, iPhone, and Android!
Stripe Billing - A set of tools for billing and subscriptions
Kittysplit - The easiest way of sharing costs with a group of friends
PayHere - Run a services business or startup? Charge recurring and one-off payments with beautifully designed payment forms. Get up and running in less than 5 minutes!
ihatemoney - Manage your shared expenses, easily
Square Installments - An easy way to offer monthly payment plans to your customers