FED'S

After part 9 of the main questline you unlock them. They are the same as gremaliens, but they payout presents immediately instead of after 4hrs. They give the exact same payout as tapping buildings, and they count as friend actions (so after 40 neighbors you will stop getting presents regardless if you tap on buildings or send feds). The main difference with building taps is that buildings only give presents to you (neighbors don't get any from handshakes), while feds give presents to both. So even if you finish your 40neighbor tour you can still help them by sending feds even though you won't get any presents. But neighbors can reciprocate.

I don't know if there's a limit of how many feds can be in a town at once.