There hasn't been a new god suggested in a while (well, a druid one in that FR, but not much else), so here goes:
This would work like any other god (ie: altars, conversion at Temple or another altar, no other religion at the same time), but the description would describe it as being an unbeleiver in the existing faiths, preferring to trust yourself.
Like Trog, the skills would not be Invo based. These skills would be about boosing oneself in the best possible way that can be achieved without magical or divine help.
For all intents and purposes, this would be the same as a God, with some cosmetic changes.
Piety would be Ego. Maybe Confidence, if Ego isn't quite right. Prayer would be Concentration.
Obviously, this is not a religion to care for (or even accept) sacrifices.
Piety (Ego) is gained slowly, based on exploration (kind of like gain with time, but won't go up if you remain idle). This can probably be done by increasing it a negligible amount when an unexplored square is revealed for the first time. It doesn't decay naturally, but since it is about caring for yourself, it will tend to go down if you spend a lot of time poisoned and/or sick. It may also be a good balance if you lose some (not too much) if you become enraged.
Due to the lack of normal decay, Supposing you pick up the religion on D5, if you don't do anything to cause decay, you should hit max around D18 or so (if you follow no branches). early enough to enjoy the abilities, with plenty of room to explore and gain more ego if you spend or lose some.
The powers are as follows:
Low Piety: Your regular stat gains have a fair chance of activating twice, and _very_ rarely, a third time. If this is too powerful, the chance can be lowered, or maybe the extra amount stored somewhere, and removed if you change faiths. The idea is that over time, you will be overall just sort of generically 'better' than an equivalent of your species in the same situation.
Low-Mid piety: Fast Jump: in one turn, you move two spaces, and are considered to have flown over the middle one. costs food, success chance uses EV skill or DX, whichever would be better. Might actually be useful if it took your breath away momentarily when you landed (meaning it needs it, and you can't spam the move).
Mid piety: When concentrating (praying), your lowest base stat is brought to the same number as your highest (ie, if you have 8 Str, 12 Int, and 15 Dx, while praying, your Str is 15). If this is too good, we can make it a temporary ability instead, costing some Ego (Piety).
A bit higher: Mental focus: If you gain a skill point in a skill that has above 100 aptitude, the pool cost (only for the one training chance), is refunded.
Higher still: Mule: Your carrying capacity is calculated as though you had 50% more strength than you actually have. Be careful not to lose your ego if you start carrying more stuff.
Max: Concentrated Hit: You can force your next attack (magical or physical) to critically hit, but the ego cost is pretty high, and you can only do this at (or close to) max. Probably causes some hunger too. Be careful not to do this too often, as losing the mule ability which shouldn't be too far below this could be devastating. Also, the cost is incurred even if the attack misses.
Overall, my goal was to come up with something different, that still works within the same rules, and feels like it would fit in well with what exists. I also wanted a God with abilities that felt "natural" and like they are working to improve you, whatever your skills are, and whatever race you are. This should work well with a lot of playstyles, and seems like it would be fun, without being too good. The highest piety move is supposed to be _very_ good, but still carry some risk, and not be abusable.