Older D&D

Right now we have

5e - most developed rule set with all the FG bells and whistles

4e - I have not used it but it is quite functional

3.5/Pathfinder - Not quite as feature rich as 5e, but quite well developed.

AD&D 2e - community rule set

Ad&D (I have trouble saying 1e here) 2 community rulesets

Castles and Crusades - sort of a version of AD&D with 3.5 elements tossed in

What we do not have is a version of Basic or 0D&D. Nor the few popular clones.

The main ones out there are

Sword and Wizardry (White Box is the most basic all the way up to complete, WB is 0e D&D first three books and by the time you go to complete you are pretty much at AD&D, or at least Basic). White Box and up is pretty open for use as long as you do not use the art work and White Box is particularly open. FGG and Matt Finch are both friendly to use of their rules (with appropriate credit and permissions).

Basic Fantasy - very inexpensive - free PDF and at cost printer materials. Pretty open ability to use their rules as well.

Labyrinth Lord - Basic D&D

OSRIC - AD&D

There are a few others like Lamentations of the Flame Princess and Astonishing Swordsmen and Sorcerors of Hyperborea that are somewhere in the Basic / 0D&D spectrum.

It would be very nice if we had a framework to play the older rules as there is a lot of material still being published that uses them. I cannot program well enough to write but I can fill out the rules with the materials and I can politely chase the different companies to determine ability to use the materials.

I also own a lot of stock art that could be used in the content that fleshes out the mechanics and this art can be used in even commercial products as long as I am the “publisher”.

Finally, I could even afford a small payment (in the area of $250) to help slightly incentivize any programming efforts. Compared to the actual effort required here, it is chicken feed, of course ...

What I would love to see is an effort on a basic building block rule set for these older rule sets.

I am not sure if it should layer over Core RPG, 3.5 (I have not seen any OSR rule set that uses the newer 5e SRD or OGL) or 5e. From what I can tell from the 2e AD&D rule set, using 5e is a subtractive process where you take away what is not used by the earlier rules and then add what is used.

A rule set that allowed to hit rolls and results based on AC ascending and descending and 9 to -9, applied weapon damage, allowed spells that do direct damage to apply it, and had saving throws based on the original categories covers most of the normal automatic. I would say an effects system that allowed for tagging but no actual results modifications would also help (tagged Blinded or Petrified or such as a reminder).

The next layer of complication that would be good is classes and levels that can modify to hit rolls, and a monster and spell list would help. Usable monster AC and HP and damage helps with the automation above.

I think, looking at the list, that White Box seems to have what a good, basic rules set needs to run the different flavors of D&D.

I will stop there, but will make another post once I get some programmers feedback on what is actually possible.

I would love some tools for OD&D as that is by far my favorite version of the game. I have to admit, though, that OD&D is so simple that I feel fine running it without any fancy ruleset to back it up.

Most of the AD&D Core ruleset will do what you need with some minor adjustments for the save system and being able to use ascending AND descending AC. I've been thinking about adding in a "race" option into classes so you could also have a "Class as Race" or "Race as Class". You'd probably want to "hide" the kits/skill/weapon profs as well (I dont recall if S&W or OD&D has some of those).

I've looked at S&W and far as I could tell it's a combat is based around a THACO system as well (they might not call it that) so that's an easy go. For something that uses a matrix style you would need to pass around some data for the attack action and then reference it... tho I'm not sure what system you're looking for.