So I discovered PEG.js a few weeks ago and I was instantly smitten writing my own toy languages. Lispy things, pythonic things, all kinds of things. The demo is pretty good for playing around with things but after a while it's fairly constrictive when I want my grammar to emit AST nodes.
So I thought, why not hack something together that glues all the different cool npm modules out there into a real IDE? So I did and it's called Hyperglot. Using a series of Ace editors, you specify your input grammar, test it out with your toy language and then view the resultant AST / JS output. After that you can go on to export your grammar into a fully-fledged compiler (ok, there are some restrictions).
This 0.0.1 release is basically just a prototype and has some annoying faults and bugs, but I've noticed how much faster it is to generate valid ASTs that generate valid JS. The next part I'll be tackling is the management of data in the application, since right now it's all per-editor localStorage.