1. The most basic use is increasing the damage with each adrenaline point. Not sure about the exact percentage per point.
Skills related uses.
2. General (yellow) tree - Rage Management skill allows to cast a sign (standard, not alternate mode) when stamina is not full by using one adrenaline point.
3. General (yellow) tree - Focus skill increases not only the damage dealt by swords but also sign intensity with each adrenaline point.
4. Combat (red) tree - Whirl and Rend skills. Each adrenaline point can be used to extend the duration of the special attack after depleting stamina.
5. Combat (red) tree - Undying skill. It's kinda bugged, doesn't work like the description says. It should prevent death when vitality reaches zero, maxed out 5/5 should restore it slightly even with no adrenaline points, with at least one point which is used then it should restore it in 100%. But mostly no matter if it's maxed out or left at 1/5 and the amount of adrenaline points it restores about 10-15% of vitality. Totally not worth it.
6. Combat (red) tree - Flood of Anger skill allows to cast a fully upgraded sign with sign intensity increased by using 3 adrenaline points.
7. Combat (red) tree - Deadly Precision skill. Each adrenaline point increase the chance of instant kill. Max 8% chance (with Superior Maribor Forest potion which gives one additionall point). Probably the best skill which uses adrenaline, especially combined with Whirl.
8. Alchemy (green) tree - Hunter Instinct. With adrenaline points at maximum critical hits damage against targeted enemy is increased (by 100% when maxed out 5/5). But this requires couple more things, correct oil applied and using Superior Thunderbolt for critical hits.
Potions related uses.
9. Superior Blizzard potion. With adrenaline points at maximum (3/3 or 4/4 with Superior Maribor Forest potion) actions don't use stamina. This can be used to spam signs or for infinite Whirl.
Of course there is a must have skill when it comes to adrenaline. Resolve - maxed out provide no adrenaline loss after taking damage.