In that case, there is nothing really cloud specific here... you just need to build a standard web app or web service that accepts user input and runs some calculations in the background. Any Rails or Django tutorial will be a good start. If you expect large jobs that require a lot of number crunching in the background then running jobs in batches with Hadoop or MPI are good options. In Rails, you can use delayed_job, SQS, or any of the other work queue systems out there to handle the background tasks.