I want some sort of pop-up or message display for things like appointments, due dates, etc. Maybe send a notice to email. Preferably something that will go out about two weeks or more.
Check out Google Calendar. You can get email and/or pop up notifications, as many as you want, at as many times before the event as you want. (There may be some limit, but I haven’t tried to find it.) Several calendar programs that you can use locally can be configured to synchronize with Google Calendar.
There are security/privacy concerns with keeping some part of your life on Google’s computer that you’ll have to decide for yourself.