Double check against player that resigned/timeout.

I think the current way it works with double check which includes a player that resigned/timed out is weird and should be removed. I saw a game where 2 players were remaining, but there was also a king left from a player that resigned. Normally trying to capture that king as quick as possible is a good idea, but it was a queen ending where the player with initiative could create a lot of checks against the enemy king which included double checks against both kings. After being behind almost 20 points the score lead quickly shifted and when he finally stopped giving checks and took the king the game was pretty much over.

One more thing that is kind of unintuitive is that the double check does not count if you leave a piece threatening a king that left, but counts if you move a piece that was already threatening the king to another square that threatens the king.

I'm overall not super enthusiastic of these rules since it really messes up the maximum score you can get, but at the very least I do not think double checks and triple checks should count the kings that has resigned.

Okay @Martin0, that was left in intentionally, but we will remove the double checks on kings from players already out of the game.

Ok 

A secondary question: how does these double check rules work when a discovered attack is made by an enemy piece.

An example: Red moves a piece which checks yellow, but also opens a line for a blue piece to check green. Does this count as a double check?

I know blue can capture greens king, but if he creates a check against both red and green with another piece instead, will he be rewarded for double check or triple check (the check on blue was not new, but just remained).

I'm not sure what you are asking, but I think this is what you are asking? Double and triple checks must be made in 1 move. If a player moves a piece that allows a discovered attack on another player's king and at the same time checks another king (be it by discovery or standard check), that is a double check (even if it wasn't his piece). The same applies for triple checks

Ok, that did indeed answer the question. Intuitively I thought it was the amount of kings my pieces threatened at the end of my turn that mattered, which is why I was confused. I get how it works now though.

One more thought. Maybe triple checks should be worth 20 points and maybe there should be a limit how many times you can get points for a double and triple check. Like each player can get points for a maximum of 4 double checks and 1 triple check. This is to prevent infinite points scenarios.

Yes @chadnilsen the king can be captured for +20

Wow ok nice.

In addition if red moved Re8+ it counts as a double check, even though one of the checks (by the bishop) was not made by a red piece.

So realistically red will get 5 points for the double check and 5 points for capturing the bishop (10 points in total), while blue will get 20 points, but lose his bishop and green will be out of the game.

A player who already resigned/forfeited on time loses. However, if you lose, you're probably about to think that you might come in 4th/3rd place if it's 4 player chess and if it's standard chess then you're lose the game, if it's stalemate or repeated moves (or whatever) then that's a draw, a 1/2-1/2. Chess is the one of the oldest and most known games to play ( brilliant, great chess move, best, excellent, good, book, miss, mistake, inaccuracy, blunder.).