I've been using matter.js to help encourage my kids to learn to program in light of the recent school closure here in the UK.

Excellent resource that gives you interesting instant feedback. Reminds me of learning Basic in the 80's.

What made you chose matter over others, say phaser? I'm building a p2p thing and want to build some showcase simple apps on it

The way I understand you could use phaser and matter.js together, matter being the physics engine for phaser. Out of the box matter.js already has a renderer so I simply didn't want to learn 2 frameworks at the same time. Once I reach a point where matter is not enough I'll consider a bigger more feature rich framework like phaser or pixi.