How do I share Processing apps with an expired signature?
An application in the form of a .app file is actually a folder containing lots of different files and folders that make up the resources of the application. To keep them all nice and tidy for Mac OS X, you can bundle them all together in a Disk Image .dmg file which can more easily be manipulated by non-Mac systems without getting the details messed up when brought back to the Mac.

Some quick directions copied from a reference listed later:


Make a folder with the files your DMG will contain.
Open Disk Utility (It's in /Applications/Utilities/)
Go to File > New > New Image from Folder (Cmd + Shift + N)
Choose the folder containing you files
Make sure "Compressed" is checked, then set where you want to save the created DMG


You can create the DMG file out of the .app file directly since the .app file is already a directory. 

More detailed info about alternatives and command line directions are at https://stackoverflow.com/questions/367751/creating-a-dmg as well as http://blog.nngafook.com/2012/07/app-to-dmg/