With all custom fields, an easy-to-use jQuery-inspired API, and a powerful selector engine, ProcessWire will rise to any task.

ProcessWire is a free PHP5 content management system and framework (open source CMS/CMF) built to save you time and work the way you do. Stop trying to bend other open source CMS platforms to your will – ProcessWire gives simpler and stronger control over your pages, fields, templates and markup at any scale. And it provides a powerful template system that works the way you already do. ProcessWire’s jQuery-inspired API makes working with your content easy and enjoyable. Managing and developing a site in ProcessWire is shockingly simple–and fun–compared to what you may be used to. What makes ProcessWire different?

via Open Source CMS with Custom Fields & API: ProcessWire CMS/CMF.