Some fun ideas in here! Instead of a tree swing, how about hanging something more grown up (but equally fun)? This inverted papasan chair base serves as an innovative place to hang curtain panels - good ideas for yard sale or thrift store finds
If your deck or patio is partially covered, drape lengths of fabric or canvas between the joists to create shade. Space out the pieces of fabric for a more transparent look, and add lights to illuminate the space at night.