In recent years, considerable effort has been recently exerted to explore the high-precision RF-tracking systems indoors to satisfy various real-world demands. However, such systems are tailored for a particular type of device (e.g., RFID, WSN or Wi-Fi). With the rapid development of the Internet of Things (IoT), various new wireless protocols (e.g., LoRa, Sigfox, and NB-IoT) have been proposed to accommodate different demands. The coexistence of multiple types of IoT devices forces users to deploy multiple tracking systems in a warehouse or a smart home where various IoT devices are running, which causes huge additional costs in installation and maintenance. To address this issue, this work presents iArk, which is a general-purpose tracking platform for all types of IoT devices working at the ultra high frequency band. Our innovation lies in the design of the "K+1"-model hardware, the protocol free middleware, and the multipath resistant learnware. By the virtue of decoupling from wireless protocols, iArk also allows researchers to concentrate on developing a new tracking algorithm without considering the protocol diversity. To date, the platform can support five mainstream types of IoT devices (i.e., NB-IoT, LoRa, RFID, Sigfox and Zigbee) and is scalable to other types with minimal effort.