Keeping track of dated events

There are a number of things that need to happen in the future at a certain date or period.
For instance, end of contracts, expiration of certificates, decommissioning of resources, etc.
Tickets have no date so it's not enough.

Until now, we've been mostly relying on assigning those things to one person and she's in charge of tracking it (via an event in one's calendar I guess).
We've also created workflows to be triggered at specific times, but it's very cumbersome to create.
Another idea is to add it to the monthly routine check but it's extra work every month and that only applies to technical stuff.

We thus need a tool where one can set a date and we get reminded later.
That sounds like a Calendar? Sure but we have no shared Calendar ATM. Should we create one? Is there a better tool for this job? @Popolechien are you using something already?

No files, tests, or implementation entry points are named. Start by resolving whether a shared calendar or another tool is preferred, then define the reminder, date/period, ownership, and notification requirements. Done means the project has an agreed approach for tracking future events and a clear implementation scope.