We're starting to open up a rest api to allow users to develop trading robots and assistants. Unlike betfair we don't charge you for access or limit the number of requests. The more activity in our markets the better - we know our infrastructure can take it.
The core functionality is already up and running at api.smarkets.com . Documentation is temporarily housed at http://apidocs.s3-external-3.amazonaws.com/index.html . If something is broken or doesn't make sense you can get hold of me at jamie.brandon@smarkets.com or jamii in #erlang.
Unfortunately we can't accept money from users in the USA due to the rather draconian gambling laws, but you can still open an account and get read-only access to the api.
The smarkets backend is built on top of erlang, couchdb, postgres, rabbitmq and mochiweb. I will be writing about various parts of our tech over the next couple of weeks at scattered-thoughts.net . Whilst this stuff gets a lot of hype there is often a lack of real-world experience reports, especially for couchdb. Hopefully I can close that gap a little bit.
Also, we're hiring: http://smarkets.com/about/internships/ http://smarkets.com/about/jobs/