As for the Calendly alternative instance - have you heard of cal.com? It's free for individuals.
I recently wrote this article featuring their origin story: <https://blog.scoutflo.com/cal-com-the-coolest-open-source-al...>
I love the Cal.com story. What gives me some pause is that they're VC-backed. $25M Series A. The free tier might be great, and I might come to rely upon it. But they're expected to produce an outsized ROI, and the traditional SaaS play is to give it away for free to capture the market and then raise prices. I'd much prefer a community-driven effort where we have no ROI expectations, so it can remain low-cost forever as we're just splitting overhead.
we will never raise prices for the free plan, free stays free, especially since it's open source which means if we were to raise, it would compete with the self-hosted product and we really dont want that
rest assured, we are comfortable providing a free product with enterprise customers
You'll also find something called OSS Friends on this page - featuring more COSS startups in the ecosystem.