I've mentioned Memotome.com in previous posts and it's an essential part of my productivity toolkit. It sends me email reminders of tasks I want/need to do, birthdays and anniversaries to remember, and pretty much handles most any recurring task.
The site has been around for a long time and I doubt that it's changed its visual design since the early 2000's, when I first heard of it. There are plenty of other reminder sites that will ping you via email or SMS, and they look prettier, operate a little more smoothly, and offer more enhanced services than Memotome. But I came to the party with Memotome, it's been utterly reliable all that time, and I resist the idea of starting over somewhere else.
Google Calendar holds my weekly schedule and one-time only appointments I schedule on the fly. Goodtodo manages portions of my to-do list for work and home, and provides a way for me to schedule a task for the future very quickly with the assurance it will pop up exactly when I want it to.
Memotome occupies that gray sort of area where I want to be reminded of things but I don't want to see them on a calendar. These are items I can set and forget.
Yes, Google Calendar lets you create secondary calendars that you can turn on and off, but I find Google Calendar increasingly complicated and its settings page for a new event almost bewilders me with all the choices. Goodtodo is great for quickie todo tasks, but its recurring functionality is not as flexible as I'd like; I want some items to recur forever, but Goodtodo limits me to a maximum of 99 recurrences, for example. Also, its emails arrive in plaintext so if I include a URL in the body of the reminder, it does not arrive as a live link.
Memotome is plain but it hits a sweetspot for me. It does not offer some features that other services offer: weekday only reminders, weekend only, "every other day/week/month," and so on. So I have to get clever and create multiple reminders to get around that limitation (such as creating two weekly recurrences, one for Tuesday and one for Thursday).
One feature it offers that I like: "every few weeks." When I'm trying to encourage a new habit, I like a once-in-a-while reminder for me to check in with myself.
You can use the service for free, but donating whatever amount you think the service is worth upgrades you to a level where the email reminders are a little more useful (your event title is the email subject line, URLs included in the body of the reminder become live links, etc). Check it out.