[somebody_amzn]

For Windows 10 Mobile, app sideloading with any signature has been implemented since the beginning. You can just install a .appx(bundle) directly, with no dev account system being present unlike WP8(.1).

[fps_doug]

True, that part was specific to WP8(.1), which is actually my favorite. It just seems so lean and no-nonsense, very unmicrosofty.