The internet lets us communicate extremely fast, so sometimes we can expect extremely fast responses without realising there's a human, living their own life, at the other end.
In today's hectic world, friends may want to reach out to friends without making them feel like they owe a fast reply; like writing a postcard.
Ending any message with "slow.fyi" does just that, because it brings them here, where they can read this message and know a reply is appreciated, not expected.
Enjoy the internet a little slower today,
slow.fyi