The short version
Open-source scheduling tool positioned as a Cal.com replacement.
From the HackerLinks archive
Thunderbird Appointment
Open-source scheduling tool positioned as a Cal.com replacement.
At a glance:
First seen:2026-04-16
Last seen:2026-04-16
Times seen:1
Website:github.com
Why it caught our attention
A Thunderbird maintainer explicitly pitched it as the open-source replacement path.
Where it surfaced on Hacker News
2026-04-16
Editorial paraphrase
“Our scheduling tool, Thunderbird Appointment, will always be open source” and “We’ll help you replace Cal.com”.
Original threadCal.com is going closed source
Also surfaced in this discussion