Comment by throwaway787544

Actually I disagree. Any time there's an Open Source tool that does everything for free, it's extremely hard to justify paying for a proprietary product that does it much better, because companies are cheap. There's many open source projects like this that are just terrible but a company will always use them first because they're free.

The answer isn't modularity, it's composeability, which is a significant difference. A modular program requires "integration" (tight coupling of APIs/ABIs) whereas a composeable program has loose interfaces which require virtually no "integration".

Drone.io is one example; you can implement any "plugin" purely by creating a container with an initial CMD entry that reads environment variables, and that program can interface back with Drone a number of ways (STDIN/STDOUT, REST API, database). Another is any application that just reads in or spits out simple line-by-line instructions or a JSON blob. Unix pipe based programs are the penultimate example. The dumber the interface, the easier it is to compose.