Compatability depends on the libraries that are required by the compiled application. For the Sharp/Cacko rom for example which runs Qtopia and uses glib 2.2.2, anything that is compatible with that will run. Some additional libraries might be required, but most qpe apps will run and the older pdaXrom packages will also work. Even the X applications in pdaXrom will run if X/Qt is installed. However, the newer packages for the kathrin releases in pdaXrom are not compatible with the stock Sharp/Cacko rom due to the difference in soft float use and/or glib versions incompatabilities in some of the applications. But despite that, a lot of ipk packages work.