There is no particular reason why Tiled no longer works on OS X 10.6, other than that I’m just compiling it with the latest version of Qt and Xcode on the latest version of OS X and this is what happens. You can try compiling it yourself with whatever version of Qt still works on OS X 10.6. I’m not sure which is the last one, but it needs to be at least Qt 4.7 for Tiled to compile with it.