Please comment and point out any obvious gaps; I'm currently putting together a game.
These are still a work in progress.
General*
Hit dice are always maxed. Rationale: the difference between dice is on average 1 hitpoint, since 1d4 averages to 2.5 and 1d6 to 3.5 and 1d8 to 4.5 and 1 d10 to 5.5. This means the fighter on average gets 3 extra hitpoints per level over the wizard on an otherwise similar chassis (2 skill-points, 1 good save). Maxing the hit dice doubles that to 6 per level.
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Base Skill Points are increased by 50%. So if you would get 2+int you instead get 3+int and if you would get 8+int you would instead get 12+int. Rationale: Int is too much of a determining factor in how many skill-points one gets which weakens the rouge compared to the wizard. Now skill-monkeys have at least a few more skill-points than the wizard.
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No 4x Skills at first level, but a +3 'rank' bonus for class skills with ranks in them. Skills are limited by HD. I dislike first level being special, and the complications of have different skill lists when building a character, so I adopted this pathfinder-ism. Now cross-class skills don't cost double ranks, but just one rank, but they don't get a +3 bonus for being class skills. The +3 bonus counts as ranks for the purposes of prerequisites and anything else that uses ranks.
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Psionics > Sorcerer Casting > Wizard Casting I prefer to deal with Psionics over Vancian casting, and if there is vancian casting sorcerer-like with a small fixed selection is preferable over wizard casting. Also one quick note on psionics, infinite power loops don't work.
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Nightsticks don't stack. They raise your maximum number of uses for the day, so if you use one and then drop it you can have more uses of turn undead used than you have as maximum and that's fine. This applies to all siomilar tricks like temporarily raising charisma and other abilities limited like turn undead. (eg use wis times per day, or con+3 times per day or whatever)
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Anything even resembling the polymorph subschool better have a good explanation for itself. This also covers wildshape and similar things. Alternate form and change shape will be subjected to scrutiny but are more likely to pass through. There might be a custom errata per instance for this ability, such as the succubus being limited to an approved set of humanoids but gaining the ability to also disguise their gear, or something while a Phasm would probably be banned outright.
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Homebrew is encouraged. But there are some ground-rules. First please make sure the class/feat/discipline/whatever is well written, eg unambiguous, it also helps if it has better grammar and spelling than my own writing. It helps if you write down your interpretation of the rules and how it compares to similar classes either in the party or in published books. It is preferred that you use homebrew someone else made, rather than your own, but if you wish to use your own you must tell me that you made it.
An example of a comparison, lets take the Disciple of Mym C'sil.
It's a charisma based factotum knockoff with a lesser skill selection and no spell like abilities but instead it gets all good saves and full bab in addition to a wide variety of fixed effects. This sounds a bit much so lets dig deeper.
He gets a monk-like but better armor bonus but is restricted from a wide array of magical item slots.
At 2'nd level he basically gets to imitate the psychic warrior Call Weapon, but it automatically scales and lets you select enchantment bonuses too. This is worrisome because it allows things like Bane (Current Enemy) but lets move on.
Beyond that he gains the ability to add cha again to AC for one round some DR/- and some teleport abilities (dimension door and a 1/day greater teleport).
In addition he gains a wide variety of minor abilities such as woodland stride and feather fall at will.
Clearly this is meant as a beatstick compared to the more versatile and sneaky factotum.
Verdict: Overall the abilities are level appropriate, the only major point of concern is the at will enchantment bonuses, shrinking it to an approved list takes care of that though, and depending on the rest of the party at will bane might very well be appropriate.
Tome of Battle*
The ninefold path. You can only have 9 disciplines, through any combination of effect whether they be learned maneuver, maneuvers granted by item or anything else there can't be more than nine, and they are not swapable. So if you gave up devoted spirit to use a homebrew discipline you can never again use a devoted spirit maneuver.
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The Prerequisites are maneuver level/3, rounded down. In short 1'st and 2'nd level maneuvers have no prerequisites, 3'rd, 4'th and 5'th have a 1 maneuver prerequisite and 9'th have a 3 maneuver prerequisite. Treat this as an errata to all maneuvers.
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Initiator Level is per discipline. So swordsage gives full level to 6 different schools while the Shadow sun ninja PrC only gives full level to Shadow Hand and Setting Sun and half level IL to all other disciplines. So if you made a 2 Swordsage/2 Warblade/2 Crusader build you would have an IL of 6 (2+2+2) for Stone Dragon Maneuvers but only 4 (1+2+1) for Iron Heart Maneuvers. Similarly the Swordsage Stone Dragon Maneuvers would count towards the prerequisites of the Warblade and Crusader selection of those maneuvers.