Zend Tehcnologies will be releasing tomorrow (Wed, April 12th) the latest version of their "code protection utility" - Zend Guard 4.
Zend Guard 4 offers an unprecedented level of code protection and a complete license management solution for the distribution of PHP applications. Zend improved the Guard product line to minimize the risk of reverse engineering by increasing protection during the encoding phase.
Zend Guard has two parts to it - the encoder and the license manager for your scripts. You can quickly and easily distribute your encoded scripts to the masses, and licenses can be easily updated/renewed without having to send out anything new. Some of the license options include concurrent users, time limitations, and if it needs to be server-specific or not.
Look for the release of this product tomorrow on the Zend website.