It’s not technically retro but I’ve found Pico-8 a great way to build retro like games! It’s pretends to be a console of a bygone era and gives a bunch of restrictions on size of game and 128x128 resolution.

The app comes with a pixel editor, sfx and music editor, and a code editor built in. The games are easy to share and you can play them on a mobile browser. On the downside, it costs 15 dollars for the app.