The Commodore 64 is the best selling personal computer of all time. Over 10,000+ programs were written for it, both commerically and in public domain circles. Sold between 20-25 million units during its remarkable lifetime (1982-1992).
http://www.commodore.ca/products/c64/commodore_64.htm
The hardware was quite capable, but the BASIC dialect was relatively limited. To really take exploit the machine's power, you had to write machine code. This was in stark contrast with the Acorn BBC.
One page links to Commodore64:
