Classes determine the main abilities and traits of your Cube World character.

Specializations
Each class can choose one out of two specializations, which changes playstyle and abilities of that class.
Skill trees
With each gained level, players can assign skill points to a skill tree. There are class specific skills like attacks or spells, and common skills like climbing, hang gliding, or pet riding.
Infinite Progression
Not only worlds are infinite, but so are you character's progression. This means players can theoretically level up infinitely and put infinitely many skill points into their skill trees. However, this doesn't mean that players can become infinitely powerful. The power of players, creatures, items and skills doesn't scale linearly or exponentially with the level, but it scales tangentially. So while levels can be between 1 and infinity, the corresponding power is between 1 and 100. A power of 100 can only be reached with an infinite level. In lower levels, power increments are more notable than in higher levels.
This system has two advantages: First, there's no level cap and the player never has the feeling of having reached the end of the game. Second, power cannot be infinite. For each land, the game generates creatures and dungeons evenly in all power ranges (1-100). That way the player can freely travel from land to land and can always be sure to find creatures and dungeons of his power.
The available classes (along wih their specializations) are shown below.