Interchange

Every part you need is already on the board. None of them are where they belong.

Drag a part to an empty cell to move it. Drop it onto another and they swap. Nothing
rotates — every piece already faces the right way, so the only question is where it
goes.

A circuit closes when a source reaches a terminal of its own colour. Later levels run
six circuits through one board, and they can never touch. Use every part. Leave one
stranded and the board stays dark.

100 levels, from three pieces to fifty-five. Every one built from a real solution and
verified solvable.

No timers. No lives. No score. No text. Just a board and the number of the level
you're on.