I haven't worked on them in a while to be honest, but for many years I worked on a small snail simulation in my spare time and blogged about it[0]. The project had gone through JS, PHP, and later Go iterations. I also spent a few weeks playing around with implementing an approach described in this paper on open ended simulations[1]. Go was not the best language to choose for this project[2], but it definitely counted as fun hobby coding for me.