I use many things and apps. Google Calendar for meetings and far dates likes birthdays. I use asana.com for stuff in the project and ideas for that project. I use Google Keep for today tasks or groceries. A paper at my desk to draw future plans. A small notepad for meeting with my bosses. And comment starting with "@todo" or "@fixme" in my code that looks like a standard since a long time ago in my experience.
Oh, for weird things I wake up Google Assistent and say to remember this thing and the time.. Like... "OK Google, remember me to scanner my family old photos tomorrow at 9 of morning"
For repeating tasks like feed my dog or brush my teeth (yes I forget that) I use a android app called HabitHub so a can click at the notification "step" and I'll only be remembered in the next time (night in this case) and save statistics that I never open to see.
For important and/or annoying emails I use the Gmail feature "snooze" which is pretty safe since it act like received again but not as unread.