This is called a "Flying Lemur" though they do not actually fly and are not lemurs. These are, however, one of the most bizarre animals on earth. Hard to even explain but here goes: at the bottom of it's body, the lump just off the trunk of the tree is actually it's kneecaps. It's knees are built backwards from ours. It has two legs that extend up from there under it's body against the tree. You can sort of see it's lower right claw. By straightening it's knees, it will "hop" up the tree then it's front 2 hands grab up higher. So basically they hop up trees like a kangaroo hops on the ground. Once they get to up higher, they eat fruits then extend all their limbs to glide like a flying squirrel to the next tree.
Below is a side shot to try to show what else they look like. One strange animal!
Kinabatan River area, Borneo - Malayasia August 2018