What are some alternatives?
When comparing Pixel Pix and PICO-8, you can also consider the following products
Responsive Pixel Art - It's exactly that... responsive pixel art 🙃
TIC-80 - TIC-80 is a fantasy computer where you can make, play and share tiny games.
Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Pixel Vision 8 - 8-bit fantasy console built on top of an open source C# SDK
piCSSel-art - Draw pixel art with CSS!
8bitworkshop - Online IDE for Atari 2600 development based on Javatari.