In most games and RPGs, there are abilities that you can get based on any number of things you have done with the character.
Diablo and World of Warcraft had the skill tree, were based on level and other abilities, you could learn new ones. The down side is that you can't learn them all. This is seen also in Sonny to some extent.
Final Fantasy 10 had a large map were everyone started some were else in rings of spells and upgrades, and you had to move around like a game board in a direction to learn spells and abilities.
Final Fantasy 12 had a hidden card game were you revealed the cards around the one you learned, and could move in the directions.
A few other games had abilities and spells that upgraded when you used them a lot.
Others like Civilization and such had prerequisites. Were you had to have one or two abilities before you could learn another. Similar to the other trees, but different.
Ok, to the point. Have you ever thought of a different way to do a skill tree? I think making it a mini game would be cool, but I haven't seen anyone do it. Post your ideas :3
I like the games where you can learn everything, even if it takes a long time. Like RuneScape. You don't have to pigeon hole yourself by only choosing one profession.