Griff was designed for the Microsoft PocketPC platform. Here's a list of compatible operating systems:
Operating System Name Good for Griff ?
PocketPC 2000 Yes
PocketPC 2002 Yes
PocketPC 2003 Yes
Windows Mobile 5 for PocketPC Yes
Windows Mobile Professional Untested (But should work)
Windows Mobile Classic Untested (But should work)
Smartphone No
Windows Mobile Standard No (It's a smartphone)
Palm OS No
Symbian No
In short, Griff is compatible with every PocketPC based device. Microsoft have done an amazing job of maintaining compatibility whilst changing the operating system.

HOWEVER Griff was designed and optimised for the screen dimensions of the original PocketPC, 240x320, otherwise known as QVGA. Since then, devices have appeared with square screens, landscape screens and vga. Although Griff will run on these devices, the display may be compromised.
Screen Dimensions Name Good for Griff ?
240x320 QVGA Yes
320x240 QVGA Landscape No
480x640 VGA Yes
640x480 VGA Landscape No
240x240 QVGA Square No
480x480 VGA Square No