In OSS, it appears nobody wants to be responsible for sending email invitations. icsinvite does this for you.
icsinvite is designed to watch a calendar collection and send invites to attendees when it detects changes.
icsmailer stands on the shoulders of:
[^1]: Over the years, I've tried 17 different flag libraries, if you include the stdlib
flag. Lately, I've been using @cosiners. While I do not prefer the "parse-into-structs" model, @cosiner's library is a nice compromize between features, size (2300 LOC), and dependencies (1, another 600 LOC @cosiner utility package). @thatisuday's commando is a close second (1447 LOC, 1 utility dep), but I find it more verbose and it doesn't support 12-factor-style environment parameters.