I've posted mainly on Linkedin, some relevant SaaS Facebook groups, and two online communities (Swipe Files and Growth Mentor). The reactions were really really motivating, and the traffic I was able to generate just with a few posts was quite impressive.
My website was only the Airtable preview (with a couple of columns locked) and a signup form to get notified when I release the PRO version (paid).
Results - over 340 users, mainly from the United States, the most qualitative traffic came from the online communities, especially from Corey Haines' Swipe Files - with an average time on page of over 40s (it was only a header with the Airtable preview).