The Xsolla PHP SDK by Xsolla integrates payments into applications. Resources include UI customization, client for API methods, and webhook server. Billing, monetization, and conversion are the services provided by Xsolla.
SumUp, a mobile payments rising star, recently announced an API that allows third party apps to accept credit card and cash payments without leaving the app. Prior to the API, SumUp users and customers were required to use the SumUp app in isolation from the merchant app to utilize the slick mobile payments platform.
Geeklist offers developers an online haven to present their work, connect with other developers, and gain credit for achievements. Geeklist's lean staff proudly states that Geeklist was "[b]uilt by developers, for developers... we make geeks lives better every day." The API allows developers to create their own applications and services and retrieve any needed data from the Geeklist database. The API has remained in private beta since the Geeklist's original launch, but will open to the public with a 48-hour hackathon from November 30 - December 3.