Maybe you'd want to have a look at Simitless. If I understand your question correctly, it should fit what you are looking for:
- uses a declarative data model,
- supports OAuth/SSO with Facebook, Google, LinkedIn, Microsoft, Slack, Twitter,
- enables you to create your own database management web app - it gives you modules/fields (like spreadsheet columns) that you can select from and tailor the app to track/collect only the data you need,
- I think it has quite an intuitive and flexible UI as well,
- uses noSQL backend (you said it would be ok as well),
- you can have as many parallel connections as you want (checks your multi-user requirement),
- has quite a few templates to choose from when building your own data web app.
Here is a screenshot of how one of the templates with dummy data looks like:
May be a worth a look.
Full disclosure: I am part of the startup that designed that platform. We just launched recently, still in beta. If you want to try it out and need some help, I can definitely give you a hand.