Earlier quoted context omitted.
I use the free tier as a collaborative Kanban board for a tiny 5 person team. Airtable allows me to define arbitrary fields for the Kanban cards, which happens to be a premium/paid feature in all the actual Kanban saas tools (Trello, etc).
It isn't on Jira if you're <10 users, but Jira is a whole lot more than just Kanban and a huge beast.
We're an academic research lab that also happens to do contractual work for other labs (mostly internal to the university), mostly designing and building mechanical prototypes and testbeds for other researchers.
It took like 5 minutes to set up an airtable base to track our WIP and all information we use for billing our "customers": hours, material purchased, internal budget reference, etc.