Me and a few others use Paint.Net. Really useful for sprite creation.

If you don't have Windows, Piskel works as well.

I use in a site called make a 8bit art is too good to use

I've tried it, and i've made the conclusion make a 8bit art really is too good to use. So good, that I have in fact vowed to uninstall and disassociate with every other editing software I have ever used.

When I opened the website up, immediately a tear was brought to my eye from the stunning beauty of the program. 'Where was this all of my life'? 'Why settle for mediocrity when beauty was right in front of my eyes the entire time'? The astonishingly easy-to-handle layout, the marvelous accessibility, it puts everything that I have ever known to shame.

Every other option is far inferior to Lolman's incredible yet unrivaled suggestion. It is the only platform for spriting that should exist, in this universe or another.

Paint.net's a pretty great starting tool if you're on Windows. Medibang is probably the best you're gonna be able to get on Mac.

I also use paint.net for my sprite edits and I'll continue to use it as I start making original sprites

I Usually use Pixilart, Its not that good but it helps me alot.