Ultimate Tic-Tac-Toe for two players, on a big board made of nine small 3x3 boards. The square you play in decides which small board your opponent plays in next. About 10 minutes. You can practice against the CPU.
Kai-oi, the Japanese shell-matching game also known as kai-awase. Find the shell whose pattern matches the one in the center, from photos of 26 real clam pairs. 1-6 players, about 10 min, CPU and solo play. On a budget, we used clams from AEON Mall Higashikurume, not hamaguri.
Three pool games in the browser: Eight-ball, Nine-ball and Rotation. Each is for two players and takes about 10 minutes. You can practice against the CPU.
Crokinole: flick your discs from the outer line of a round wooden board. The nearer the centre, the higher the score, and the centre hole is worth 20. For two players, about 15 minutes, with a CPU opponent.
Four-Player Chess (Free-for-All): four players on one board, all against each other. Captures score points and checkmate scores 20. About 35 minutes. CPU players can fill seats.
Bughouse Chess for four players in two teams. Partners play opposite colors on separate boards, and captured pieces can be dropped onto empty squares. About 10 minutes. CPU players can fill seats.
Snakes and Ladders on BoardGameJoin: roll one die and move from 1 to 100. For 2 to 6 players, about 10 minutes, with CPU opponents available. Snakes and ladders act only on the square where you stop.
Three-Player Mahjong in your browser: three seats, 108 tiles, no chi, north tiles can be set aside. Play with friends or against two CPU opponents. Scores are calculated automatically. About 25 minutes.