Gravatar is a service for providing globally unique avatars and was created by Tom Preston-Werner. It is owned by Automattic, having integrated it into their WordPress.com blogging platform.
Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScript.
jQuery is a cross-platform JavaScript library designed to simplify the client-side scripting of HTML. It is free, open-source software using the permissive MIT License. Web analysis indicates that it is the most widely deployed JavaScript library by a large margin.
PayPal is a global eCommerce platform for buyers & sellers. PayPal allows payments & money transfers to be made securely via email, phone, text message or Skype.
Stripe is an online payment processing tool for internet businesses. Stripe handles everything, including storing cards, subscriptions, and direct payouts to their bank account. Meticulously designed APIs and functionality help users create the best possible product for their users.