I’ve been using Spreedly for NeoBudget since November 2008. Their service has saved me countless hours and headaches, and I’m immensely thankful. I highly recommend their product if you’re creating any type of subscription based service.
Since I was an early adopter of Spreedly, there was no PHP implementation of their API so I created one. Feel free to use it, fork it, do whatever you need.
Latest release: v2.6 (February 5, 2010)
Issues (report bugs and request features)
ChangeLog (view change history)
Source (read through the source code)
Download (download and use it yourself)