PEAR Channels provide a robust and effective way of distributing development. The addition of channel support to the PEAR installer as of version 1.4.0 means that it is now simpler to distribute any PHP code project using the PEAR installer than it ever was. PEAR Channels allow developers of applications to effectively depend upon packages from pear.php.net and any other source that provides a channel server. For users of these applications, this eliminates the complexity of installation and configuration. Now, all the user will need to do is to type a single pear install channel/Packagename command and go!
Before PEAR 1.4.0, the only solution to depending on code from several sources is to bundle the code. This has several bad side effects, the most obvious of which is that code size increases dramatically, and makes upgrading for a minor bug fix a complicated download for the user.
Channels allow an application developer to depend on packages from pear.php.net, a package from pear.example.com, and others. The user will only need to install/upgrade from a single source using the pear installer. With the current state of affairs, the pear installer is only really useful for installing, well, PEAR packages. Because of this difficulty (among others), traditionally very few packages are available as PEAR packages that can be installed with the PEAR installer.
PEAR 1.4.0+ aims to eliminate this and other barriers to application development.
Documentation is not yet complete