For most older adults, their own homes is the overwhelmingly preferred environment for living and growing older. However, for those living in homes with stairs, the difficulty and risk of injury in stair ascent/descent is a major challenge in their daily life, which may endanger the feasibility of such choice. In this paper, the authors present a novel assistive device, namely RailBot, to help mobility-challenged individuals (including frail older adults) to climb stairs more easily. Unlike the traditional elevators and stair lifts, the RailBot is a highly compact device that can be easily installed in existing stairways, allowing it to benefit a large number of individuals living in homes with stairs. Further, by assisting the users' stair climbing instead of carrying them upstairs, the RailBot enables and encourages the users to maintain and enhance their stair-climbing capabilities, and thus contributes to their long-term physical health. The design details of the RailBot prototype are presented, including the system configuration, the actuation mechanism of the mobile platform, as well as the intuitive control interface for start-stop control and speed regulation. After mounting the prototype in a real-world use environment, a small-scale human study was conducted, with the results clearly demonstrating the effectiveness of the RailBot assistance through the significant reduction of lower-limb muscle activities.