As mentioned by the author, Evolutions
is an effort inspired by a rather obscure SNES release with similar gameplay elements. Starting off as a microscopic lifeform, you must eat your way up the food chain while avoiding creatures larger than you from causing any harm.
The status bar shows your current energy, which can be replenished by eating smaller organisms. A cocoon will appear once you have consumed enough food. Guide your avatar into it for a growth spurt and perhaps a new ability or two.
It's still a work in progress but the demo does allow you to sample just enough before kicking you back to the desktop.