SabreDAV is the most popular WebDAV framework for PHP. Use it to create WebDAV, CalDAV and CardDAV servers.

Full documentation can be found on the website:

http://sabre.io/

branch	status	minimum PHP version
master		PHP 5.5
3.1		PHP 5.5
3.0		PHP 5.4
2.1		PHP 5.4
2.0		PHP 5.4
1.8		PHP 5.3
1.7		PHP 5.3
1.6		PHP 5.3

SabreDAV is being developed by fruux. Drop us a line for commercial services or enterprise support.