One of many features Hack/Mine introduces to Minecraft is a stat system. It currently includes Strength, Agility (now defunct), Dexterity, Intelligence, Wisdom, and Fortitude. While the mechanics are mostly in place, the balance still has a long way to go (That's what alphas are for!)
Leveling and Experience
Each player begins at level 1. By killing monsters, players gain experience, which in turn increases their level. The experience required to level up increases with each level (and was more than quadrupled with patch 0.5.) The planned level cap is level 30, though currently there is no limit in place.
Currently, all experience given by a defeated enemy is based on whoever dealt the killing blow; this will soon be replaced with a more fair, damage-tracking system, but for the time being makes for no experience when the mob dies from fall, lava, or poison damage.
Players do not lose experience, levels, or items on death (though they will take a 10% durability penalty to all items in singleplayer).
With each level up, the player gains 5 points to use to increase their stats. If points are not spent between level ups they stack up for later distribution.
Strength increases melee damage by .5 per point. It may soon affect things like mining and digging efficiency, among other manual processes.
Agility is currently not implemented in the game. It may be added in a future update, possibly gaining some of the numerous bonuses from Dexterity.
Dexterity increases Defense by 1 per 5 points. Crit Chance is currently the only stat to feature diminishing returns, however, the amount of protection given by defense becomes less and less, the more you level up. So for example, 15 defense might have given 20% at a certain level but if you level up it might only give 19% damage reduction. This might potentially mean that players would have to invest some points into fortitude of they are to survive the late game. Dexterity currently affects a lot of things, so splitting it into both Dexterity and Agility is an ongoing possibility.
Intelligence increases magic damage by .5 per point and general spell ability. At the moment, the only things that constitute "magic damage" are the Wand's projectiles and the bonus elemental damage on weapons. The Mage's spells also increase damage with intelligence, but at a differing rate.
Wisdom increases total mana by 10 per point. Note that the rate of mana regeneration is a fixed percentage of total mana.
Fortitude increases total health by 12 per point for the Warrior, 7 per point for the Mage, and 10 per point for the Ranger. Note that the rate of health regeneration is a fixed percentage of total health, 3% of the Max HP rounded down at the decimal. As discussed above in the dexterity section, because of the nerf to defense, fortitude might become a bigger priority. Also due to the introduction of the ability tree, abilities will now scale up in damage with ability points and stat points can be put into fortitude instead.
Stats and Spells
Ability damage scales off the item you have on your hand so if you have a lot of intelligence and you're holding a wand using whirlwind, your damage would scale with that.
However, I am not sure if mage abilities scale purely off their item in hand.
Currently, Strength is a completely useless skill for the more advanced player, who specializes in bows and wands rather than swords, despite choosing Warrior as their class build. Dexterity is one of the better stats for rather obvious reasons, but so is Intelligence, because of the added damage when using weapons (or armor, in the case of the unique item "rugged cross") that stacks. Regarding the damage bonuses from intel, a player sporting a wand with 3 or 4 elemental damage types (These are very, very rare and require large villages with numerous vendors to acquire in a reasonable amount of time) can expect to see their damage per point increase by 2 or 3, versus the puny 0.5 rewarded by Dexterity and Strength. Dexterity is also best used for its defense, and crit in addition to damage. Fortitude's worth had gone up significantly after the changes to defense, as defense has now become more of a early game stat and for late game survivability, players only have fortitude to look towards. Wisdom is actually quite crucial throughout the course of the game as you would be relying on abilities to deal damage and running out of mana would be the worst thing possible.