Proll is a 2.x PROM compatible replacement for JavaStations, that can be used on emulators such as Qemu or to make possible to boot Linux, as later 3.x series of the PROMs are unable to boot it.
JavaStations came with two different PROMs installed in them. Version 2.30 shipped with the earliest Mr. Coffee models, that was updated by latter versions of the Sun Netra J software environment to 3.11. Krups and Espresso came with 3.x versions of the PROM by default.