Betfair have an API for users. It used to be free but they've started charging for it now. I did experiment with it on US sports (MLB, NBA, NHL) a few years ago when it was free. It was pretty cool, put the money in your account and your phone (in my case) done the rest. However, as it was dealing with just one exchange you did have to programme with price:select criteria which, in my case, didn't prove profitable so I lost interest. However, the fact that they're charging for API access proves that you're probably betting against computer programmers as much as against other punters these days.
Far cry from the days when the exchange in the IFSC - Betdaq, I think - used to wine, dine and freeroll prominent market makers!