Last time i was looking for something as simple as possible and available everywhere I cared I landed on ruby (not rails) CGI with Forms and hooked it up to whichever http server was lying around. I expect it to keep running with minimal maintenance in 20 years.

Forms are everywhere: contact forms, support forms, feedback forms, ...

For startups, it is important to monitor and quickly respond to events like sign ups or form submissions. This post explains the different options to handle form submissions without managing the backend yourself.