FICSing some tactics

Here's a fantastic position I saw in a FICS game last night. We'll skip the early part of the game and get to the interesting bit - far be it from me to admonish anyone's opening play when they can get to this sort of position!

hangbuik (2074) vs Kashniganbaruda (2100)
White to move

White's pieces are clearly better placed, and while both Queens are unprotected, Black's has a defensive role... 19. Rxd5 Bh6+ 20. Kb1 Rd8 this seems like a reasonable idea, surely the Rook must move now? 21. Nf5.

hangbuik (2074) vs Kashniganbaruda (2100)

Black to move

Quite an amazing position! White's Rook and Knight can both be captured by a pawn or the Queen, but his back rank is weak...

If the Knight is captured, taking the Queen or Rxd8+ are both good. After Qxd5 there's a fork with Ne7+, and after 21. ... cxd5 22. Qxd7 Rxd7 23. Re8+ with mate to follow. Meanwhile White threatens both Rxd7 and Nxh6+.

Black thought for a few minutes before wisely choosing 21. ... resigns.