In small saucepan over medium-high heat, bring rum, sugar cane and cinnamon to boil. (If not using rum, substitute with water.) Boil, stirring occasionally, until sugar dissolves and liquid reduces to ¼ cup, about 3 minutes. Remove from heat; let cool to room temperature. (Note: this sauce can be stored, covered, in the refrigerator, for up to 1 week.)
Alternately thread pineapples, strawberries, kiwis and mangos on 12 skewers.
Heat grill to medium-high heat. Brush fruit skewers all over with rum sauce. Place skewers on clean, greased grill grates. Cook, brushing with sauce and flipping occasionally, until fruit is charred and tender, about 5 minutes. Serve warm or at room temperature.
For a chewable skewer and a sweet presentation, use sugarcane sticks instead of wooden skewers to thread fruit. Sugarcane sticks, available in the produce section of most Latin and Asian markets, specialty food markets, and online, are pieces of fresh sugarcane that have been cut into skewer-like pieces. Use them in place of wooden or metal skewers to grill fruit, shrimp, scallops and chicken for a subtly sweet taste. Use unused skewers as stirring sticks for summer drinks and cocktails.