I mentioned I'll be running a S&W version of Rappan Athuk for some friends. The first session is supposed to be August 1st and then go every other Friday. Hopefully. But I figured I'd post about some of my house rules. This is a fairly long post.
I'll probably miss some because I don't really have a list of them. I've taken the text of S&W: Whitebox (which is a retro clone of 0e D&D for those that don't know) and just added the information from various blogs and other systems. Much of it is taken word for word from other systems, which is why I don't want to just post the document.
Attributes give no bonuses to attack, armor class, or number of spells known. Strength gives a number on a d6 that you have to roll higher than to perform any strength feat (bending bars, forcing a door, etc). Dex does the same, except for dexterous feats (stealth, picking locks, etc). Intelligence gives a d6 Lore check, Wisdom is a d6 Notice check, Charisma is a d6 Persuasion check, and Constitution gives a HP Modifier. Intelligence is also the number of bonus languages you start with as well as the max spell level you can cast. Charisma also is the number of relatively loyal henchmen you can have.
Classes are Fighters (d8 HD up to level 9, then +2 HP), Mages (d4+1 at first level, then d4 up to level 9, then +1 HP), and Thieves (d6 HD up to level 9, then +1 HP).
Fighters have a target number on a d6 that gets better as they level up to perform Fighter Stunts (pretty much any combat thing that's not an attack). They also only have one attack unless they take the Rapid Strike or Rapid Shot feat from the list of Fighter Feats that I stole from Delta (except they get one at level one, four, and ever four levels afterward). Saving Throws start at 14 and get better every two levels (max 5).
Mages memorize spells as they do in 5e, except its equal to 2 + your level. Saving Throws start at 15 and get better every two levels (max of 6). They can wear any armor and use any weapon, but cannot cast spells in armor or if wielding a two handed weapon and suffer a -1 damage penalty with all weapons (minimum 1 damage).
Thieves can activate their sneak attack as they do in 5e and add 1d6 damage, which increases at levels 5, 9, 13, and 17. Their Saving Throws start at 13 and get better every two levels (max of 4). They get 2 points to spend between the skills Climb, Locks, Stealth, Traps, Notice, and Slight of Hand and 1 point every odd level. You add your skill ranks to any Dex Feat (or Notice roll) when applicable. No skill can have more than 4 points. At 3rd level, they can read most languages on a 5+. They can use any weapon and armor, but the heavier armors interfere with their skills and they cannot use their sneak attack ability when wielding medium or great weapons.
Elves and Dwarves are as written, except that they can only reach level 5 as thieves and I use the optional Elf class instead of allowing separate Fighters and Mages.
I use a silver standard, but have messed with the prices of a few things to make them more or less expensive as I wanted. (I divide the coin treasure by 10 to keep the balance).
Weapons are Minor (1d3 damage, but can be hidden easily, 1/2 encumbrance point), Light (1d6-1, minimum 1, 1 encumbrance point) Medium (1d6, +1 damage if using two hands, 1 encumbrance point), and Great (1d6+2, two-handed, 1 1/2 encumbrance points). I use these damages instead of polygonal mainly because the +'s to 1d6, on average, are equal to the d8 and d10, but you can't roll 1's. Which make them nastier as far as I'm concerned.
Thrown Weapons have a range of 10' (no penalty), 20' (-2 to attack), 30' (-4 to attack). Missile weapons have a range of 30' (no penalty), 60' (-2 to attack), 120' (-4 to attack). You get a +4 if the target is immobile.
I use Ascending Armor Class and Attack Bonuses (modified from the Whitebox rules, but pretty close. At level 10, a Fighter has a +7, Thieves have a +5, and Mages have a +3) rather than THAC0, mainly because I think its easier. Unarmored is AC 10, Leather AC 12, Chain AC 14, Plate AC 16, and Shields give a +1.
Combat round is as follows:
1) GM determines suprize.
2) Declare Spells
3) Each side rolls 1d6, highest goes first. In the event of a tie, PC's act before monsters and NPCs unless there's a good reason.
4) Each side, in initiative order, fires missiles and can finish spells of levels 1 and 2.
5) Each side, in initiative order, can move.
6) Each side, in initiative order, can finish spells of level 3 or higher. If an archer is unengaged and didn't move, he can fire a second time.
8) Start the next round.
Reach weapons can attack from the second rank, but require two hands and only deal 1d6 damage.
If your DEX is at least 13 and you use two minor or light weapons, you can dual wield them to gain a +1 to attack. Fighters can choose to parry instead by making a successful Fighter Stunt roll to instead gain a +1 AC for the round.
If you don't choose to attack or take any action besides move, you gain a +4 bonus to AC
Death and Dying and Healing are as my 5e house rules.
I have a slightly modified spell list for mages that I am too lazy to post here.
That's pretty much it. It might seem like a lot. But it's mostly little things that I've already written into the rules we'll have printed out at the table. Plus I'm the only one at the table that knows how changed they are. Things might have to change once play starts, but this is the base I'm working with.