Ask HN: Open Source License Which Prevents Competing SAAS

Hi HN, I'd like to launch a product based off of some Open Source work I've done. I would like people to continue to be able to use the code for anything they'd like (commercial or non) -- provided they commit back. But most importantly I'd like to prevent people from being able to launch the software as a product, that is prevent a software as a service product, which I want to launch to help support development.

Does anyone know of appropriate licenses I can choose?

Thanks