Navtech Software (www.navsoft.co.uk) do software for the Psion range including the Revo.
I've got their Sierra 7 flight planning and (basic) moving map software running on a Psion 5mx coupled to a Garmin Etrex Summit GPS. It's untried in the aircraft yet but works a treat in a car.
[This message has been edited by G-WHISKY (edited 15 January 2001).]