This article presents the novel modular version of the robotic platform Cellulo, a versatile handheld robot initially designed as an educational robot. The use of Cellulo in different contexts and applications over the years has highlighted the need for modularity. Modularity adds versatility by increasing the spectrum of functionalities of the robot, as well as more robustness.Modulo Cellulo consists of three modules: a main module, a battery module, and an interaction module. We describe the new Modulo Cellulo platform, the different modules design, the mechanical and electrical inter-connectivity between them, the new adaptive controller, and the application development framework. As a show case, we present the addition of the reconfigurable robot Mori as a module for Cellulo, in an activity envisioning the collaboration between reconfigurable swarm robots.