The PROXmobil3 has two 1GB microSD cards by default - one facing sideways, and one facing down. The sideways one contains the rootFS, and the downways one contains the initFS.

The rootFS contains a minimal embedded install of PTXdist Linux 4.9, and is mounted read-only by default. It doesn't have much of anything beyond busybox and bash 4.3. It is difficult to remove, requiring near-complete disassembly of the unit, and it is not recommended unless you broke something.

The initFS contains the fare reader program (at /init/efad/prgm/ProxNx) and associated startup functions, and is mounted at /init during boot. If you need additional storage capacity, it is recommended to replace this microSD card and bind mount necessary paths (e.g. /home) to the initFS microSD card.

Also on the initFS seem to be old versions of the CapMetro software? At /init/install/archive are files suffixed .X72, which seem to behave as normal zip files. A copy of ProxNx (the CapMetro software itself) is found upon extracting each one, along with associated configuration files.