There are many options we can use as reminders to make sure that we will not forgot something — appointment, paying bills, etc. Right now, for the web-based service, I use Google Calendar to manage some schedules. Most of them are sent by email.
Besides that, I also have some of them set on my phone. If you want to have a web-based service and want to have reminders sent to your email, you can try Resnooze. It’s a simple, but I think it’s pretty useful too.