Abstract Cyber-Physical Systems (CPSs) often operate in a critical context where it is crucial that they behave as intended. However, the heterogeneous nature of CPSs makes them inherently challenging to develop. To assist in the development process, one can perform co-simulation, where models of constituents of a CPS are coupled to jointly simulate the full system. The challenge herein is to combine heterogeneous formalisms in a sound fashion and address practical needs such as stability, performance, platform compatibility and so forth. To address this, Maestro is a tool for co-simulation using models adhering to the Functional Mock-up Interface standard for co-simulation. Its development was driven by needs from different industry domains such as railways, agriculture, building automation and automotive. It supports both a fixed and variable constraint-based iteration scheme along with platform distribution capabilities. The tool is open-source as an attempt to increase adoption of co-simulation and encourage researchers to collaborate. Maestro has been validated by industry through application in the aforementioned domains. It is a step in the direction of the two-folded long-term goals: ensure trustworthy co-simulation results and make co-simulation a technology taken for granted.