This paper presents a sensor fusion method for a Wi-Fi-based indoor positioning system, named the KAist Indoor LOcating System (KAILOS), which was developed to realize a global indoor positioning system (GIPS) that utilizes crowd-sourced fingerprints. KAILOS supports the deployment of indoor positioning systems in buildings by collecting indoor maps and fingerprint DBs of buildings for the GIPS. Thereby, KAILOS provides a method based on sensor fusion for volunteers to develop indoor positioning systems for their buildings. KAILOS has been made available online for public use. In addition, various location-based applications can also be developed using KAILOS.