The last time I was handing out candy at my old neighborhood, kids would ring the doorbell but then they'd just stand there and stare at me until I handed them candy. You're supposed to say "trick or treat"!
Now I live in an apartment, so I don't get trick-or-treaters. (I have candy just in case, but nobody ever knocks.) My roommate went to hang out with his sister and hand out candy at her place, and apparently their neighborhood has decreed that trick-or-treating ends at 7 sharp now so that nobody is out after dark? I don't get it. I thought staying out late (and, for teens, potentially unsupervised) was part of the fun!
Sonic Roboblast 2 Kart and its successor Dr. Robotnik's Ring Racers are open source, and pretty fun! The exact degree to which they're free-as-in-libre depends somewhat on Sega's policy of turning a blind eye to fan games, so although GPL-2.0 permits commercial use I wouldn't recommend testing it.
There is a lively modding scene (or there was for SRB2K last time I was playing it; I haven't played RR yet). Ring Racers has single-player content if that's what you're looking for, I hear it's quite challenging.