I needed a tool like RegReminder and bought the standard edition. Installing is easy. In my case I had a minor problem but this was solved very quickly. A very fast respons and solution was delivered. This extension is really excellent!
I looked for a calebder and event system.
I tried them all but there was always a problem or missing functionallity.
DPCalender was a relief: it worked, it has all you need (perhaps more than that, I got new ideas).