I know is off topic, but I was planning to use Raspberry PI to run amiga Emulator, when available, but if OS4 was ported to the Raspberry the I'm all for it.
Just look at it, $35 Amiga
Honestly forget about OS4 on the Raspberry Pi, OS4 is for PPC and it's not going anywhere

AROS on the other hand has ARM ports, and I fully intend to use the Raspberry Pi as my full time AROS machine

UAE will work on such a machine, but don't expect it to run any faster than an A500
