Being a casual linux/open-source user wanting to learn pixel art, I first learned about Aseprite, but didn't feel like investing in an app I wasn't sure I would use a lot. Pixelorama fixed that, and I'm loving it so much that I don't even think about looking elsewhere. I use it a LOT and receive news of its updates like I'm following a cool TV show. Pixelorama is just awesome.
itch.io is an open marketplace for independent game creators. It's completely free to upload your content. Read more about what we're trying to accomplish and the features we provide.