What's your rapid prototyping tool/process

Hello everyone

I am looking for new ways, processes and tools to speed up the prototyping of new applications, mostly FE apps. My goal is to have something that I can show to the business people asap before sending it to the providers to build it.

I am open to any tools or processes you think they can be of interest. I have used invision in the past but I am also interested in code generation for the prototypes.

Any ideas? Thanks