The initial idea of the Majestic Wilderlands was to publish my setting. But I quickly realized that I needed some mechanics to support specific elements of the setting. Plus I felt the best setting books had both well written background material and useful rules and items. So the result was a book half rules and half setting information.
Since I was doing this as an independent publishers, I needed to use something that was legal to use which in our neck of the wood means something under the OGL. For various reason I settled on using Swords and Wizardry as my target rule set. Since then, 2009, I ran several campaign and kept tweaking and modifying until I got to the point where why not combine into not just a supplement but a more or less complete ruleset. So that what I am in the midst of doing now and why you see the occasionally post about spell, armor and equipment which I cherry pick out of my current draft.
Doing this gave me some insight into what would be useful, if you or anybody else wanted to do this.
For something straight forward mechanically, the best place to start is with Swords and Wizardry. Matt Finch not only placed his rule book under the OGL, he went the extra mile and made a word document that you can edit for the basis of your own.
If you want something that works with Classic DnD and has more options for characters and the game but not go all the way like D20/Pathfinder. Then I would look at something like Blood and Treasure by John Slater. He doesn't have a 100% OGL system reference document but there is a lot of material that can be used.
Of course if you want to go the whole hog there is the both the d20 SRD and the Pathfinder SRD. Even if you don't use the core concepts of either SRDs, they have the equivalent of appendices that have all kinds of extra stuff like Kingdoms rules in the Pathfinder game. Stuff that could be ported over to any of the OSR games I blog about.
Doug and I both have a lot of experience with GURPS. The game is still one of my favorite RPGs. A lot of the rules in the Majestic Wilderlands are adaptations of templates and rules from my GURPS campaigns. However when designed them, where I could I opted to remain as DnDish as possible and only make the minimum change to incorporate the mechanic. Hence not a lot of opposed rolls or defenses but a lot of saving throws and to-hit versus AC.
But you know I still really like GURPS and RPGs that are skill based and has more mechanical detail than classic DnD normally does. So I tried to roll my own with Fudge but that didn't work out as well as I liked. So I just said to hell with it and started to write complete RPG based off of Sword and Wizardry and my stuff. So you know it floundered on the fact +1 using Fudge Dice is a huge bonus. It was proving too difficult to get the math right for the progression I wanted.
I did have an idea for a skill based system with mechanical detail that may help Doug or anybody else trying to do their own take. Especially they are a fan of GURPS. Understand I spend a lot of time on this so I don't how it would actually play.
- You start out with the d20 SRD
- You use 3d6 roll high from the Bell Curve Variant
- Add in Wounds and Vitaltity.
- Then shake in the ideas of Generic Classes.
Now this is just the starting point for a skill based RPG. To get the mechanical details, a designer need to look through the multitude of feats (the main mechanic of d20 to add extra abilities) and come up with a set that give you feel you want. Keep in mind how it will look at different points in the character's advancement.
Because all of the is under the OGL you can something back for your work beyond your home game whether it just sharing it or selling it.
Finally what funny is that I just finished reading Fantasy Age because my friend +Tim Shorts is into the Dragon Age RPG. What I didn't realize to that point was it used a variant of 3d6 roll high as it primary mechanic. So it was fun to see how they implemented it.
Hope this helps anybody wanted to roll their own system.