The Gibbon Rehabilitation Center seeks to repair some of the damage done to the local population of white-handed gibbons and to repopulate the local forest with the released animals. You can visit the Center for free, but as it depends on volunteers and donations, it's expected that you cough up a little something.
The story of gibbons on Phuket is a sad one. Poachers stripped the local jungle of the animals more than 30 years ago. These days when you see a gibbon, it's generally being led around in a drugged state as a tourist attraction.
At the Center, gibbons are taught how to adjust to life in the trees. They are paired with other gibbons (as often they have been kept alone, so don't know how to socialize properly) and are introduced to their natural foods.
You can watch the gibbons from a viewing platform and talk to staff about their work.
The Gibbon Rehabilitation Center is in the Khao Pra Theaw Non-Hunting Area. To get there, take Highway 4027 and head to the Bang Pae waterfall.