I sent an email to the app designer, in Netherlands. Haven't received a response.
In the meantime, I have looked up kraisydave's vocab.
Read Only Memory (ROM) refers to the phone's internal memory where your firmware/apps are stored.
Stock ROM is the software that came on the phone when you pulled it out of the box.
Popular custom ROM's (for rooted phones): CyanogenMod, Android Open Kang Project (AOKP), MIUI, Slim ICS, Liquid Smooth ROMS