A mechanical puzzle with a maze on the outside of a cylinder, with 2 rods that follow the maze, which you can slide back and forth through the central cylinder to "teleport" to the opposite side of the maze. The commercial version is manufactured in the Czech Republic by Rademic puzzles.
A server programming challenge. You get given a protocol specification, you write an implementation and host it yourself, submit your IP address and port number, and the system runs a series of automatic tests against your server to check that it works correctly.
4x4 chess puzzle
A 4x4 chess board is filled at random with the 16 chess pieces, excluding pawns. Alternating between black and white, play moves that capture an opposing piece, repeating until only the white king remains.
A 5-digit combination lock can only display prime numbers and 00001. The combination is 10723. How do you open the lock?
Fit 6 pentominoes into a rectangular grid that seems too small. 3d print it yourself.
Fit a load of cut-out circles into the shape of a cloud. 3d print it yourself.
There are more posts about puzzles in the puzzle section of the blog.