ChrisTenone:
1985: 'QuickBrownFox' for Vic-206502 processor, 1 MHz, 8K ram, program on ROM cartridge. Arduino beats this by a lot!
I ran HES Forth79 on my VIC20. I was able to write Forth words that WROTE Forth words on that VIC!
As far as Mega2560 RAM limits.... 512K external RAM giving 8 banks of 56K heap space, just under $30.