PEBL has always been cross-platform, and I designed it using the http://libsdl.org libraries as its first platform, which enables fairly easily compiling for Windows, Linux, OSX, and probably with some efforts things like Android and iPhone/iPad. Several versions ago, I stopped distributing a version for OSX because I didn't have a Mac anymore. But we recently acquired one, and so the OSX version is back, as of PEBL 0.11.
I make no promises for PEBL on OSX, especially because I've only tested it in limited situations. But it should allow the growing community of psychology researchers who use OSX to enjoy the same tests as their Windows and Linux brethren.
There are a few caveats, however. PEBL is essentially a command-line tool. This is fine for Linux, where everyone knows how to use the terminal, and can easily create launchers and such. On windows, I made a visual basic launcher that serves most people well. But I have no launcher for OSX. You can launch on OSX from the terminal, or by making a .command file (see instructions in the installer), but I also included a little drop-on script courtesy of applescript (see right). These are little application launchers that let you drag a script onto the launcher (you can put the script anywhere too), and it will launch with the specified options. Applescript is available on all OSX machines, so you should be able to edit this to do things like collect experiment options and subject numbers, launch multiple scripts, upload data afterwords, and so on.
Just as proof, here is a screenshot of PEBL running the Corsi Blocks test (it can run full-screen too):
What about PEBL for you iPad or or iPhone or Android? It should be possible, but I probably won't put the time into doing it unless I charge for it, so let me know if there is any interest.
Users have reported that the OSX version only works on 64-bit processors/architectures. If anyone has any experience cross-compiling 64-to-32-bit SDL apps using g++ on OSX, and wants to try compiling it themselves, let me know.