For more than ten years I'm the developer of mailmindr, the free Thunderbird extension for setting reminders and follow ups. I'm doing this in my free time, so if mailmindr is helpful for you please feel free to send me a donation.
Possible ways to support me
You can pick from three choices to support me:
Credit card & PayPal
You want to send a one-time donation? Or do you want to donate a small amount every month? mailmindr is using PayPal as payment provider for this, even without a PaPal account. Donate to mailmindr.
If you want to support my work on a monthly basis, there's a Patreon site for doing so. On https://patreon.com/arndissler there are some tiers available. Pick the one which suits best.
There's an amazon wishlist with some items I find useful, either for me or my kids: https://www.amazon.de/registry/wishlist/WHZ3626BZ2C7. The deal is simple: you buy an item of the list and amazon will send it to me.