Why does this not support downloading? Because it's too much work to implement, and this was a fun little project I made in an hour.
How does it work? Simply upload an image, use the inputs, and adjust it to your heart's desire. Want the image? Take a screenshot.
Do I plan to add anything else? Most likely not, but we'll see.
Can I trust you won't steal my files? Inspect the codebase on GitHub; it's right there. Just don't steal my code, haha.
Does it support HEIC files? No, it supports PNG, JPEG, JPG, etc.