In this thesis, we introduce the concept of cell-sized integrated systems. These systems are created by integrating dissimilar micro-devices, offering diverse functionalities akin to those of macro-scale systems but scaled down to the size of a single cell. The two primary types of cell-sized integrated systems are micro neural implants and omni-enviro autonomous micro-robots, creating both of which face distinct challenges. The creation of micro-neural implants is limited by constraints in manufacturing technology, requiring a universal method to combine various functional microscale devices. The challenge in developing omni-enviro autonomous microrobots lies in the absence of certain components: high-efficiency micro-actuators that can operate in all environments. In this work, I will demonstrate how we overcome these challenges by introducing a heterogeneous integration method for combining disparate microscale devices, and by developing a new type of micro-actuator. After addressing these challenges, I will showcase our advancements towards the goals of creating micro neural implants and autonomous microrobots.