GP2X vs. GP32
This is an old side-by-side photo comparison of the GP2X and GP32 open gaming handhelds made by GamePark in the 2000s.
The GP2X was a milestone at its time: embedded Linux OS on ARM, 64MB RAM when my laptop had 128, SD/SDHC cards for storage instead of the fragile and limited Smart Media Cards. The older GP32 had better build quality, finer controls, superior ergonomics, and a shorter boot time thanks to its custom bare-bones OS.
Both used replaceable and rechargeable AA batteries, and most importantly both had a free SDK that encouraged users to port and create their own software to share with each other.