How to quickly make a web site for start-up experiments

Periodically, my friends and I have ideas for web startups.
Often ideas are simple, but they require some kind of site infrastructure - for example, user registration.

I would like to be able to run around ideas - to create prototypes during the evening.

We ourselves do not know local JavaScript and do not know any client side technologies, but we know Java, Groovy - i.e. we can write logic on server side in these languages. Well, if you need something in PHP, Ruby is also writing something simple with a textbook in your hands.
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What are the features to quickly create simple sites?

WordPress what else and how to fasten your logic to it?
Any site builders?
Frameworks?

Thank!