Optimum Loading Screens turns Minecraft's loading screens into a resource-pack format. Any pack that ships a manifold.json takes over the boot screen, world loading, world upgrades, server connects, and every other loading or waiting screen.
No config files, no menus: install the mod, use a texturepack which contains a loading screen, done.
.mcmeta frame-strip conventionScreens without measurable progress (connecting to a server, waiting on a response) get a sweeping bar instead of a fake percentage, automatically. No need to configure.
Three official themes are available: Neo-Glitch, Cinematic Dawn, and Badlands Edition (fully animated: a minecart rolling into a badlands sunset).
Making your own theme needs no code; it's a folder with a JSON file and some PNGs. The complete guide: PACK_AUTHORS.md.
Inspired by icehunter. Provenance record: attribution.