Jotform is a popular form builder, but I had to separate Jotform Apps into their own tool because they're actually really decent.

It's incredibly easy to use, and it's got the basics for a simple build.

What I'm most impressed with, though, is you get an unlimited number of users, and an unlimited number of push notifications on the free plan.

That's rare as hell. Push notifications are never on the free plan, let alone an unlimited amount of them.

You don't get much design flexibility, and you don't get much advanced functionality (although they do have an embed block, so you could embed other tools)

But they're integrated with Jotform's top-of-the-line form builder, so if you need to:

1) Collect information from your users

2) Send them notifications

Then Jotform apps has what you need, and likely for free.