The repository is less then stellar in telling one how to do it, yet there are a ton of packages out there. I would like to create my own, how is it done?
PXL format doesn't appear to be documented, but fundamentally it is a zip file with a directory structure (the source to be installed) and a special plist (PxlPkg.plist) that is an XML file containing instructions for installation.
Unzip some existing PXL files to see what can be done - dropbear.pxl has postflight instructions, for example.
There also preremove instructions to be executed before removing an application.