For others, like myself, that looked into this thread to see how the OP solved the issue, I will provide what I did when I opened the disk image only to find no *.app.
The original help file for installation appears to be deprecated, as the new disk image only contains two folders. While this might not be the expected procedure by the developers, and with the lack of installation documentation, the trial and error method of dragging the Planeshift folder to an appropriate folder in my home directory. I put it in Application but I doubt that I will keep it there on subsequent "installs". However, once it is copied, then open that folder in the new place and run the pslaunch. The first step was to have it update itself, so let it update and restart. Then, it appears to need to update again (possibly to update the game files) which takes a bit longer. Once it has updated twice (note, it does this twice with 0.5.1, so future releases this may not be true, so the number of updates may not be the same), and doesn't seem to want to update anymore, then I went to the settings and adjusted my display and other things appropriately. Then I hit run and the pslaunch died. Not to be undaunted, I tried the other application in that folder, which presumably is the game and it started up and ran.
That is all I did, and I am at the initial tutorial zone. Seems to work, but I haven't done anything else yet.
