The idea of Remind is to have every scheduled event of your life in a plain text file (or a collection of plain text files). Remind is like a markup-language for time and it supports extremely complicated rules for repeating events (like: garbage is collected on mondays every two weeks, but not if the monday is a holiday in which case the garbage is collected on the following tuesday - in any case remind me the evening before the actual day to put out the trash can). And if your scheduling demands exceed Reminds language features, you can use its internal Turing-complete API for setting up your own rules.
In my opinion there is nothing better than a plain text file for keeping scheduled events and I am obsessive with my Remind files. As a software developer, I have my text editors (VSC + Emacs) open all day and there is no faster way to write down an event than typing a line in my Remind file. I probably used more than 50 calendar tools in my life - standalone and cloud based. In many of them it was simply ridiculous how complicated it was to enter an event with reminder and repition rules: mouseclick after mouseclick, popup after popup, clicking tiny arrow-icons eleven times to set the month to November ;-)
I collect EVERY event of my life, sometimes many years in advance (for example, my Remind files contain the expiry dates of all important documents, end dates of subscriptions with their respective cancellation periods, anniversaries and such).
Next, Remind is a command line application, that allows to display the contents of the Remind files as calendars in the Terminal or export them for a given time range. The export options include different versions of plain text and HTML and whatever else the Remind community came up with. I made my own script, that utilizes the Remind CLI to produce an interactive HTML-calender with 5 different themes exactly to my specifications.
With Remind I own a consistent diary of every scheduled event of my life in the last 20 years. I never forget a birthday, miss a deadline or accidentally renew a subscription. My raw data is readable in a text file. I have full control over backups and encryption and my data will be usable even if Remind ceases to exist one day.