Idle games require almost no input from you: progress accumulates automatically while you're busy with other things or even while the game is turned off. You come back, spend your progress on upgrades, and everything grows even faster. These are clickers, resource farms, and endless progression games that are great to keep open in the background.
These are closely related concepts: incremental games are about constantly growing numbers, while idle games are about growth happening without your input. Most often, a game is both.
Any of these games can be downloaded via torrent, repack, portable version, or GOG release.