Need MRP software recommendations

Hi All,

I have a customer who has a Windows/Citrix based MRP
(Manufacturing, Requirement, Purchases [I think])
program, who is tired of all the rebooting and crashing.
He has 65 Windows clients on his network.

He asked me if I know of a Linux (server) based replacement.
He has looked a little at SAP, but I think it overwhelms him
a bit (expensive too). So, I told him I'd ask you guys if
you had any you liked. Any and all recommendations are appreciated
(what works and what to avoid).

Many thanks,
-T