I technically could just use the standard six of Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma. It is the generic system for any thing based off of D&D which anything roleplaying generally is but it has some weaknesses, especially for a computer based game.
Lately in the back of my mind I have been tossing around a three ability system with sub-stats. Each main ability would have two stats that come from it in a way similar to how AD&D 2nd edition player options (skills and powers) book let you split abilities. A good example of it is that Dexterity has the sub-abilities of Aim and Balance so after you have your Dexterity you can change those so that you could have a clumsy ranger that can hit anything. Before this if you wanted to hit anything you also had to be able to balance on anything. Of course with six abilities each having two sub-abilities you end up with the possibility of having 18 different abilities to track. I will admit though that breaking up Charisma into Leadership and Appearance is nice for IRL roleplaying games. Of course there is a limit on how big of a difference you can have between the two sub-abilities (4) and they do have a minimum of 3 and max of 18(barring strength) but that is mostly to reign in people from making their characters the ugliest hags on the planet just so they can rule the planet.
For my system I don't know quite how much of a difference I will allow but for now I will just use 4. The three base abilities themselves will be something for overall strength and toughness, something for the overall ability to move and your manual dexterity, and finally something for your overall mental ability. I am quite tempted to name them mostly after abilities already around like having the physical one be Strength but that does not quite fit as it will also be representing toughness and the preconceived notions that people will bring to my game could cause confusion. My current names for the main abilities and their sub-abilities are as follows:
I do use a few abilities names that are already common but only where it does basically what it does in other systems so it does not matter in those cases. I did try to come up with other names for them but in the end the ones I used just described what I wanted to say the clearest.
One of the things I plan to do with this setup is that I can make the base three abilities hard to raise permanently and have the only dependable way is through level up which fits my plan of starting with only three classes available.
As for what they do I have a rough outline in my head and will post about it later once I have it nailed down some more.