there are also some online alternatives, like:
pixilart -
https://www.pixilart.com/ (also avaiable on google play and apple app stores, can import palettes but insertin color values manually!)
piskel -
https://www.piskelapp.com/ (supports palette importing and also animation, there is an offline version too avaiable to download)
Closing notes: older aseprite versions, up to 0.9.5 are legally downloadable too, here:
https://www.aseprite.org/older-versions/only win, mac and linux versions, no android one but source code for compiling is avaiable...as for such verison there is no rotating tool nor an import palette function, the only way to achieve the latter is open an image with the oxce palette and then paste/draw in it :'(
bonus: if you're nostalgic try
deluxe paint 2 online! (works only on desktop pc)
Edit: openxcom palettes can be found
here