A combinatorial strategy game
The board is a row of numbered squares. A set of coins is placed on distinct squares at the start of the game.
On your turn, move one coin to any unoccupied square to a square with a lower number.
The player who cannot move loses — that happens when every coin is already on the lowest-numbered square it can reach without landing on another coin.
Coins can be moved by clicking (select a coin, then click the destination) or by dragging.
Welter's Game is a classic combinatorial game studied in 1954 by C. P. Welter.
Source code is available at
codeberg.org/fuglede/welter.