Rocks'n'Diamonds

I want to know so bad!!

From what I understand, it was originally just built off of Mirror Magic's code structure, while Mirror Magic was a sort of "port" of Mindbender built just on SDL. I don't think there's much behind that.
I may be wrong on that, so Holger, feel free to correct me on that.

Rocks'n'diamonds as far as I understand is not based on any existing game engines (like godot, unity, etc.,) but built on top of sdl for cross platform multimedia capabilities. It is in a sense a meta engine for building boulderdash type of games and currently uses integrated native engines for playing levelsets of boulderdash (gdash), emerald mines (x11 emerald mine) and Supaplex (megaplex).

Its earliest versions are for linux (1995)and dos (1998). Contemporary game engines did not exist back then

Thanks, Vikits, yes, that's all correct. And also TheOnyxGuy perfectly described R'n'D's origins.

Indeed the earliest incarnation of R'n'D's code base dates back to around 1988, when I wrote "Mirror Magic" in C for the Amiga.

In 1994/1995, I ported that game to Linux with X11, and then created R'n'D as a sort of "spin-off" with a different game engine (which, as Vikits correctly described, was written from scratch and is not based on any existing game engine, because at that time there were no such "game engines" to be used out there ). A few years later, Guido Schulz (a colleague of mine at that time) added support for MS-DOS by using the Allegro game library. Some more years later, I added support for Windows and Mac by using the SDL libraries. Even more years later, I added support for Android by using the SDL2 libraries (and finally also support for running R'n'D in web browsers). Over the years, I removed support for native X11, Allegro and SDL (version 1.2) for easier maintenance.

As of now, R'n'D only has SDL2 (and a few related SDL2 libraries) as its only dependencies, which makes it easy to port to systems it currently may not support yet. (The currently missing support for iOS has no technical reasons, but is just due to the fact that I (a) don't want to pay $99 per year for writing a free and open source game, and (b) because it is not possible to write your own software for iOS without using Apple's closed eco system. But maybe this will change one day... )