• See skins and hear sounds in any version that supports it
• Use online mode in versions <a1.0.16; b1.7.3> (NOTICE: It is risky to let legacy Minecraft versions to send your profile's sessionid through an unencrypted connection. If you're a server owner, better toggle online-mode off)
• Save and load your levels online in Classic versions

• Login with both Mojang and Microsoft accounts for online servers
• Play Indev with sound
• Choose from all currently available legacy versions (over 180 more than in other launchers)
• Easily toggle the proxy
• Get a Discord RPC status when playing the game
• Save your Classic levels offline (with an ability to load them to a server & vice-versa)
• Use addons to customize your game without modifying game files:
  • GameModeSwitch - toggles the gamemode switch in versions <c0.28; a1.0.0>
  • QuitGame - toggles the "Quit Game" button in versions <b1.0; 1.5.2>
  • Fullscreen - makes Classic & early Indev versions go fullscreen! <rd-132011; in-20100110>
  • OfflineDATSave - toggles local level loading & saving code <c0.0.13a_03; c0.30-c-renew>
  • Demo - toggles demo mode in versions <12w16a; 1.5.2>
  • ClassicNotPaid - toggles the "Premium only!" message in c0.30 versions
  • UnlicensedCopy - toggles the "Unlicensed Copy :(" message in versions <b1.6-test_build_3; b1.7.3>
• Easily set game resolution in Classic versions <c0.0.12a-dev; c0.30-c-renew>
• Use basic instance features:
  • Set the game's directory
  • Set the game's resolution
  • Name your instance
  • Change the icon of a game's window
  • Add custom JVM arguments
  • Remove and create new instances
• Download mods from the mods repository (it ensures they're going to work)
• Join servers from the servers list (and external ones too)
• Set the launcher's language

The launcher supports Windows, MacOS and most of Linux distributions.
The newest version can be found here.

Simply download the launcher and double click it. It's very easy.