OpenTTD

OpenTTD is a sandbox transport simulation based on Chris Sawyer's Transport Tycoon Deluxe. It mimics the original as closely as possible while extending it with new features, tasking you with building and running road, rail, sea, and air networks to move freight and passengers for profit.

Games can be played solo or in multiplayer, cooperatively or competitively, and a wealth of add-on content - new vehicles, industries, scenarios, and AI opponents - can be fetched in-game from the Check Online Content menu. The game ships with free base graphics, sound, and music sets, so the original Transport Tycoon Deluxe is not required, though its data files can still be used if you own them.

OpenTTD runs on Windows, macOS, and Linux. Its code is GNU GPL v2.0 (with some bundled third-party components under other licenses), and it is free to download from the official site, Steam, GOG.com, and the Microsoft Store.