Cryptpad has Forms. You can choose if users need to sign in. Looks like you don't even need an account to create one on their official instance. It's self-hostable too.
In case, you're looking to do polls or schedule an event, then FramaDate is also pretty good. You can find a hosted instance at https://nuudel.digitalcourage.de/ .
One of the most useful features of Google Forms is automatically transferring the form input to a spreadsheet. Any of FOSS alternatives have that ability?