Minecraft Indev Launcher [2021] -

Betacraft is the industry leader for legacy versions. While known for Alpha/Beta, its Indev support is flawless.

Modern Minecraft launchers (like the official Mojang launcher) do not support Indev natively. If you try to load an Indev JAR through the vanilla launcher, it will crash instantly. This is where the becomes essential. Minecraft Indev Launcher

In the "Version" dropdown, scroll to the bottom. Look for versions starting with Specifically, look for old_alpha indev-20100223 (or similar dates like Launch & Play , then hover over the new profile and hit Betacraft is the industry leader for legacy versions