They allow you to bestow random kindness on someone else on the same street. The receiver gets a nice rainbow overheard that says "random kindness" and some harp music plays (or you know what I mean) AND 50 energy. (I think it's energy; might be xp.). :)
I think you get it from harvesting crops if you have Croppery III skill (and yes they pop out like weeds when harvesting) and I think receiver of random kindness gets +50 energy or +50 mood depending on what they're lowest on. Got mine from Jethimadh though