The classic free and open source sim OpenTTD, based upon the popular Microprose game "Transport Tycoon Deluxe" has now entered a feature freeze period with the first Release Candidate out for the upcoming major update.
OpenTTD 1.10.0-RC1 went out a few days ago and while they're now not including new features due to the freeze, this version does have plenty in it. Features like supplying a reason to people who get kicked/banned when playing online, item highlighting under the mouse cursor in the file browser, a separate window for taking screenshots, the ability to configure the game ending year, the ability to take a full mini-map screenshot, logic improvements for sharing industry production between 3 or more stations, a cargo filter for the industry directory window and there's plenty of crash-bugs that got solved.
It's shaping up to be a really big release now especially with all the modernisation going on with the code like the newer SDL 2 video driver added in a previous beta, multiple big performance improvements are in, more flexible docks and plenty more.
You don't need data files from anything else to enjoy OpenTTD, as it has plenty of free graphics sets available as well as sound/music too. However, you can use the Transport Tycoon Deluxe data files too. See more on the official OpenTTD website.