Like others everything is in both my phone and my work outlook calendar.
As soon as school newsletter/emails come in with dates they immediately go in and then get copied to my work calendar.
My iPhone uploads to the our so all the reminders are on DH's phone too and vice versa.
All the children's extra curricular activities, party invites, docs & dentist appointments as well as birthday, anniversaries and bill deadlines are set, with reminders.
For birthdays a reminder pops up a week before to give me time to buy a card/present and then another reminder 2 days before to post it.
Like lots of MNers I have small children, work long hours and have a myriad of hobbies, friends, activities and events to keep track of.
The only way everyone (including the adults) is in the right place, at the right time, with the correct clothes and equipment is because everything's planned in advance so I can lay it all out the night before.
It's not for everyone (my sister would hate it) but it keeps me sane, reduces stress and means we all get to do everything we want to.