+1 for remind and wyrd. Remind is really, really powerful. You can express things like an appointment that fires "every 3 weeks starting May 4th, but if that day falls on a weekend or holiday then {skip it, move it to the following/preceding weekday that isn't a holiday}", and lots more. Wyrd is a really nice console frontend to remind (I just found that there are graphical frontends available too). Finally with rem2ics you can express really complicated things in Remind and then export the results as an iCalendar-compatible format and import that into whatever other calendar you want.
I used screen, remind+wyrd, mutt, and irssi (and even ledger) in school; I got a job at a bigco that pretty much required me to use gmail and gcal, and I stopped using console things as much. Lately I've been toying around with moving my mail flow back into console / console-ish inside emacs.
- tmux
- mutt - email client
- wyrd + remind - calendar
- ledger - double-entry accounting tool
- weechat + weeslack plugin - fully featured, super fast slack from the CLI