Back in the 90's a game which appeared to be overtly influenced by D&D was generally called a fantasy heartbreaker. It was typically considered a game in which the author, having house-ruled AD&D over the years, had finally reached the point where his interpretation of the game attained special significance: it was so far removed to one degree or another from AD&D that it looked like a different game, and the author was so enmeshed in his interpretation of said game that he could not imagine any other game (including AD&D) being more worthy of consideration for play than his own.
Some of these early fantasy heartbreakers languished unpublished. In the 80's and early 90's in particular the everyday nonexistence of an internet meant that sharing your fantasy heartbreaker required publishing it through the channels available at the time, which also did not include print on demand. There was no Lulu or Onebookshelf to realize your dream. If you were savvy and talented then you could turn your heartbreaker into a real game with a real following (I consider Palladium Fantasy to be in this category, for example). If you were less talented then the results could prove interesting (If you've ever heard of World of Synnibarr it is regarded by some as on the more extreme end of the fantasy heartbreakers). Most are completely forgotten, though.
Today, fantasy heartbreakers still exist, but thanks to the transformative era of the D20 OGL 1.0a we have more "mechanically consistent" heartbreakers than ever.....we just don't call them that. The entirety of the OSR is essentially a subgenre of fantasy heartbreakers, as is every single D20 era system which thought to demonstrate that it was better and more efficient at doing D20 than D20 was (be that Fantasy Craft or Grim Tales, to name a couple). The OGL at least made it possible to comfortably do this legally, and also allowed for a unifying structural arc over the entire mess.
A side effect of this is that today we have an abundance of published and often well supported game systems which are all essentially variants on the same D&D theme, sometimes to the extent that they are collectively each fighting for a corner of the same specific experience, rather than collectively offering anything particularly new. When you have this mixed with a GM like myself who likes to collect way too many books this can lead to scenarios where it becomes, at times, troubling to think about which flavor of D&D you want to play at any given moment. Like, really annoying!
I mean, on my shelves alone I have the following (this is what I have after my great purge a couple years ago, mind you):
13th Age - for people who liked the direction of D&D 4E but didn''t want the map/minis harness.
D&D 5E - the current D&D, carefully designed to emulate how people play over what the rules said.
D&D 3.5 - the beast that started the last 20 years of gaming evolution.
D&D 0E - the original, characterized as the root of all things OSR by some.
AD&D 1E - the version associated with Gygaxian prose and endless unique subsystems.
AD&D 2E - the version I actually enjoyed playing the most for all of a decade.
Pathfinder 2E - Paizo's attempt to distinguish itself from the competition, but also my current fave.
Pathfinder 1E - the one that happened when WotC abandoned its base .
OSRIC - the first successful attempt to show how the OGL could revive old school design.
Labyrinth Lord - the OSR version for people who loved B/X D&D (and also AD&D).
Dungeon Crawl Classics - the carefully designed aesthetic and focus on procedural randomness plus unusual dice to evoke the sense of the 70's like a scratch-n-sniff that smells like your uncle's waterbed.
Mork Borg - I think this is for people who love ideas but also don't like words that explain things unless those words are grim, dark, metal, etc.
Troika! - also for people who like ideas but aren't big on coherence, and also who loved Fighting Fantasy as kids.
Palladium Fantasy - I've got the most recent edition, but would argue that Palladium is the definitive original heartbreaker.
Mythras Classic Fantasy - it might seem odd to include this, but it fits; Mythras is a Runequest based system and CF is all about changing Mythras so that you can play it like AD&D...but with more percentiles.
Swords & Wizardry Complete - the definitive OSR clone of D&D 0E, allegedly (except for all of the others), but arguably the most playable and fiddly of the different 0E variants.
....there are likely others I have forgotten about sitting in storage or whatever.
The point being: there are a lot of different systems out there currently that let you achieve your exact and highly specific brand and flavor of D&D that you want. For some reason I have a lot of them on my shelves. I have gotten rid of others in the past.....as much as I enjoy the style of play Castles & Crusades evokes, for example, it was simply too close in feel o D&D 5E for me to keep it around. There are other contemporary old school clones that are simply not quite worth the effort when the original editions are now all back in POD; why bother with For Gold & Glory, for example, when I already have all the AD&D 2E stuff I could bear?
But the real question I run in to is: why have all of these systems on my shelves to begin with? As a collector the answer is obvious: so that my relatives and family must do a lot of back-breaking cleanup in my study when I die. But aside from that.....I find that until that fateful day all these fantasy heartbreakers lead only to momentary confusion as I find each one has its merits and is worthy of attention, yet I only have so much of that to go around, and only a couple times a week to game. As such, I inevitably need to choose the games that best fit my actual playstyle, and those are only a handful, to be honest.
So....this was a long post to come around to saying that I may need to look at another Ebay selloff soon, or maybe I'll just start boxing some stuff up to clear out space and take them to the local bookstores. If I do this, I figure I'd need to let my collection settle down to the following:
1. The edition I am most likely to run consistently (Pathfinder 2E)
2. The edition I am most fond of because it does everything I want it to (D&D 3.5)
3. The edition I know is most popular so should keep for that reason alone (D&D 5E)
4. The edition with the most nostalgia and for which I actually would be willing to play again becasue of that (AD&D 2E)
There's also Dungeon Crawl Classics, which I would be inclined to keep because I feel it tries hardest to do its own thing.
The rest.....should probably go. Hmmmm. We shall see!