A 21.co program which tries dictionary attacking hashes (for a small fee).
This allows an easy monetization of the tedious task to gather and maintain a wordlist of common passwords. The "/solve" endpoint checks the hash (and salt) against the wordlist at cost. Only in case of success does the result have to be 'bought'.
The benefit of doing this through something like 21.co is that the wordlist itself does not have to be exposed.