Since vom and emacs were already proposed, there is a third classic in this round: Shell programming. Typically you have $EDITOR env set (to something like nano, vim, emacs, gedit, kwrite, etc) and then can include it in your script as in
echo stuff >> worklog
$EDITOR worklog && mailto someone
Acme: http://acme.cat-v.org/ It can do everything Emacs can but it's so lightweight it almost doesn't exist. Its power comes from the fact that it brings your external tools together.
It can be programmed using its filesystem (9p) interface, and extended by adding plumber(4) rules.
A demo by Russ Cox: https://youtu.be/dP1xVpMPn8M
emacs is the programmable text editor
Neovim with Lua should do the trick.
Could probably write VS Code extenions that do all this for you.
Emacs, Vim, a UNIX shell
emacs is socialist and bad, Neovim is social democrat and good
Just to echo a few comments, I'd use Emacs for this.
For time based events, you have the `run-at-time` function.
For snippets, I'd look at YASnippet[0] as they're really easy to create and you're granted a significant amount of control. Nothing you wrote sounds outside the scope of what it can provide.
On save is easy, just use `after-save-hook`. Emails is easy, too, though you will need SMTP or something.
Followup email may require custom code however Emacs 29 has SQLite support so you may be able to utilise that?
0: https://joaotavora.github.io/yasnippet/