Podio is as powerful a platform as Airtable. Maybe even more. From inception it was marketed as a project management tool. It is rather a very powerful no-code app builder. They have a large community of loyal users and many of them builders. Their API is super flexible. Their mobile apps mirror almost everything you can do in their web UI, through their API.
They have a large community of very loyal "nocodies" and "lowcodies".
Stacker would be a perfect fit to provide the same portal benefits where SF, AT and Podio fall short.
Please take a brief look at their API documentation > https://developers.podio.com/