Been thinking a lot about Gestalt recently, so I put together this document for a slightly different way of handling it, where you get the average progressions of your two classes.
Somebody suggested the averaging approach on this forum before, so it's not entirely original, but I've set it up a little differently and included a lot more stuff.
The document also has my character points rule, which replaces the standard feat and ability score progressions, and my multiclassing rules, which smooth things out a lot and eliminate the need for the Mystic Theurge, Eldrich Knight and Arcane Trickster.
Finally, I've included some archetypes, all of which are designed to stand on their own, but also help their classes to fit together better into gestalt combinations.
They are the Ovate Oracle (a Charisma-based spontaneous caster which uses the Druid spell list), the Hexblade Magus (a Charisma-based spontaneous caster based on the Hexcrafter), and the Ascetic Magus (a Wisdom-based magical martial artist based on the Kensai).
If your only interested in those, go ahead and scroll down to them.
Here is the document. Let me know what you think of it and please, if you have a question, ask it!
Some thoughts in no particular order.
I'd like my BAB rare, please: The BAB progressions are normally called full, 3/4 and half. What are 'poor', 'medium' and 'good'? There is such a thing as a poor and good save though, so a "medium" save makes sense.
hp vs HD: hp are not HD. Hit Dice are the number of dice. 1 level in a character will have 1 HD. hp calculation is what is being described in this section. Also the arbitrary +4hp seems strange. Why not just take the average of the two maximums at first level?
Spell levels: Each of your spellcasting classes gains a bonus level of spellcasting for every two levels you have that don’t include it. RAW this means you take 1 level of wizard and never take it again and you will have half your character level in wizard caster levels. If this is the intention, it is horribly overpowered. The spell level should only increase by 1 for every half-level of the class that gives you that spell level.
Overall For simplicity I would not allow a double gestalt. Things just start to break down. Though I do see the allure. Maybe only allow a switch on even numbers? Either way, its a good start but needs a bit of fleshing out imo. Keep it up. :)
I've always used good and poor BAB interchangeably with full and half, but you're right, I should change that.
I actually do mean hit dice. I'm literally changing the number of sides the dice have. I guess I should change the wording so it's clearer I'm talking about number of sides not number of dice?
You've missed something in the spell levels section. You can't benefit from a greater number of bonus levels of casting than your class level, so that wizard dip character would get a grand total of one extra level of spellcasting.
What do you mean by a double gestalt? A character who multiclasses between two different gestalt combinations?
Anyway, thanks for the comments. I'll make a couple of changes.
EDIT: Termollogy changes made. Actually shortens and clarifies the wording quite a bit with the BAB progressions, so that's good, but I will miss the medium-well joke.
Oh and I forgot to say: The reasons it's a +4 bonus are so it doesn't matter what order you take your classes in, and to help level the playing field between large and small HD classes at early levels.
If there's one rule you could remove without worrying, it's that one.
EDIT 2: I just realised, you think those multiclass spellcasting rules apply to everyone. That's not the case! You advance spellcasting at the full normal rate when you take gestalt levels that include a spellcasting class. You advance at half rate when you stop levelling in the class, but you can't more than double your levels of casting that way.
This rule might sound crazy, but it ends up giving 10/10 multiclassing exactly the same as the mystic theurge, eldritch knight and arcane trickster progressions, but spread evenly over 20 levels and without the class features.
The main differences are it's more versatile, you don't have to have a near-useless character until you qualify and you can't abuse it by building a gestalt who qualifies early.
Finally, I don't get what you mean by a switch on even numbers.