Aplos makes nonprofit software simple. Aplos has several stand-alone, but integrated, web-based products that can extend third party applications.
Users can turn on or off each of these Aplos products independent of each other. If more than one product is enabled, then they integrate with each other.
For example, if you are a donor management or church management software, you can simply pass Aplos the Accounting transaction. In this case, the user would only pay Aplos for use of the Accounting software and would continue to do Contributions management in your software.
If you are an online donation processor, you can pass Aplos the contribution, which would give the user the ability to do contributions management in Aplos, which would then integrate with the Accounting product if linked by the user. This means your user can continue to use your software for the donation processing, but use Aplos for contributions management, accounting, and donor management.
All you need is an Aplos account and then you can enable the API from your settings page.