Apparently:
http://www.learnchessrules.com/castling.htm

http://www.learnchessrules.com/enpass.htm

I've heard of castling before, but didn't know how it worked. I have never heard of an en-passant capture.  Glad I'm learning this stuff now, before the jam starts :P.

There are also chess variants:

https://lichess.org/variant/racingKings

https://lichess.org/variant/chess960

This website lets you play them against a bot or a friend.

Wow, En passant was completely new to me too!

Looks like it was added in the 15th century, this is what I get for not reading the patch notes!

Apparently it was a nerf added after the double-first-move made pawns too OP.

So yeah pretty much!

chess 960 is honestly terrifying

http://reallybadchess.com/ is also great

Oh and don't forget all the Stalemate/Draw rules. Some of them were new to me as well:

https://en.wikipedia.org/wiki/Stalemate

https://en.wikipedia.org/wiki/Threefold_repetition

https://en.wikipedia.org/wiki/Fifty-move_rule