I have an implementation here [0] if people want to play with it. Supports dynamically changing the controls, has obstacles and predators. Setting weights for separation, alignment and cohesion to zero and then increasing only one of them nicely shows which role each of them plays. It's actually made as a workshop [1] for my company, where the shell is provided and one has to implement it step by step. In Norwegian, though.

Update: Dang linked other discussions, and I see I commented on one from 2015 [2]. Someone there asked for the course content, and that's available (in English!) in a PDF in [1]. This workshop/implementation is actually an example of what I wanted the students to make at the time. Which I then retrofitted to a fun workshop for my colleagues.

[0]: https://matsemann.github.io/boids-workshop/ [1]: https://github.com/Matsemann/boids-workshop [2]: https://news.ycombinator.com/item?id=9300142