One of the inconveniences of PEAR is that is has no package-specific mailing lists. Thus, if you want to talk about a specific package and no other, you have to get all the traffic whether or not it is related to the package in which you are truly interested. As I said, it's an inconvenience, but having it would be a nice touch. Thank goodness for Tigris. :-)
Text_Wiki is an object-oriented PHP library to parse wiki text and then render it into any of a number of formats. Each parsing and rendering rule is its own class, so you can add/change/delete parsing rules quite easily. Aaron Wormus gives it a favorable review (thanks Aaron! :-) and provides some example code on how to write your own rules at the end of PHP Barnstormer #15.