I've been working through some ideas on the dungeoneering board game I mentioned a few days ago. Here's what I've got so far:
Characters will be made of Classes and Races. Any race can be of any class. I'm going to start out small so here's the short list of classes and races I'm pondering at the moment:
Classes will have certain abilities and weapon/armor restrictions. The abilities will be broken down much like those found in D&D 4E: At-Will for powers that can be used at any time, Encounter for powers that can only be used once per encounter, and Dungeon for power that can only be used once per dungeon. As a character levels up, they gain access to different powers.
Halfling (although when playing with my son, I'll likely refer to them as "Hobbits")
Races will grant special bonuses (and possible penalties) to attributes, possible bonus Hit Points, as well as access to special powers.
Character attributes will be simple bonuses (or minuses) that affect certain rolls or action checks.
Melee Skill: Denotes how skilled a character is at hand-to-hand combat. Weapon Skills between opponents are compared with the difference between the two being applied to the character's attack roll against Defense.
Ballistic Skill: Denotes how agile a character is as well as their skill with ranged weapons. This bonus applies to the character's Defense.
Strength: This bonus applied to melee damage. Strength bonuses are also applied to Strength checks that may be called for during the course of an adventure.
Mind: This is a measure of how smart and how willful a character is. Mind bonuses are applied to many powers of magic-using classes like Clerics and Wizards; they are also applied to a character's Mental Defense.
Defense: This is a base 10 + Ballistic Skill - any armor caps to BS. A roll equal to or higher than a foe's Defense can cause damage.
Mental Defense: This is a base 10 + Mind + any item modifiers. A roll equal to or higher than a foe's Mental Defense will allow a spell to affect him.
Hit Points: This is a measure of how much damage a character can take before dying.
Leveling up is done by earning enough gold to afford training. No XP to track. Leveling up allows the character access to greater powers as well as making dungeons more dangerous and the treasures more valuable and useful.
I'm thinking of adding a special bonus characters can choose after hitting a certain milestone (after every so many adventures) that will give them a little boost. These will range from weapon specialties to slight bonuses to treasure rolls and the like.
Items will come in Five varieties: Basic for unmagical gear that can be bought in any store in town, Uncommon for magic items with only a single prefix or suffix enchantment (Copper Sword, Helmet of Wisdom, etc.), Rare for magic items with a prefix and a suffix enchantment (Golden Sword of the Bear or Dancing Staff of Fireballs), Unique for items that have static abilities, and Artifacts which can only be discovered by top-tier characters.
That's what I'm thinking so far, but this all might change the further I get into the design process. The next step is to catalog the various monsters I have from the myriad of dungeon games in my collection as they will serve as the base monsters for the characters to fight.