Hello and welcome to the forums! I have split this from the nightly builds topic as it was not directly related to that.
Transport Tycoon Deluxe and Transport Tycoon before it were commercials game from the 1990s created by MicroProse. They were written by Chris Sawyer as a follow-up to the earlier Railroad Tycoon of 1990, which was written by Sid Mier who went on to write Civilization the following year.
Simutrans was created from scratch by Hansjorg Malthaner ("Hajo") starting in about 1997, and the first beta was released in 1999. It became open source in 2004 and has been developed by the Simutrans community ever since. Although it is similar in many ways to the Transport Tycoon series, and was inspired by it, it is a different game with an entirely distinct code-base, and is distinct in a number of its features.
Simutrans-Extended comes from a fork of Simutrans (initially called Simutrans-Experimental) that I created in 2009. It uses much of the same codebase, but differs in a number of respects set out here
The original Simutrans is sometimes referred to as Simutrans-Standard to distinguish it from Simutrans-Extended, although it is more usually simply called "Simutrans".
I hope that this clarifies matters - welcome again.