PolyMC

PolyMC is a free, open-source launcher for modded Minecraft. It is a fork of MultiMC.

History
It was forked from MultiMC because the PolyMC community felt that the maintainer of MultiMC was not acting in the spirit of free software by disallowing third-party packaging efforts. It is not endorsed by MultiMC.

It was forked again by Prism Launcher in October 2022 after the owner performed a hostile takeover, removing other maintainers for promoting "leftist queer ideology", and removing the PolyMC Code of Conduct which prohibited discrimination against the LGBTQIA+ community.

Features
Being a fork of MultiMC, PolyMC includes most, if not all, features of MultiMC, as well as some of its own. Features included in PolyMC include:
 * Simultaneous control of multiple Minecraft instances.
 * Custom icons and groups for instances.
 * Management of multiple Minecraft user profiles.
 * Ability to play offline.
 * Starting Minecraft with a custom resolution and Java arguments.
 * Changing Java's runtime options (including memory options such as MaxM and MinM).
 * Showing Minecraft's console output in a color coded window.
 * Killing Minecraft easily if it crashes or freezes.
 * Forge integration (automatic installation, version downloads, mod management).
 * Fabric integration (automatic installation, version downloads, mod management).
 * Minecraft world management, with copying and renaming features.
 * Importing and exporting Minecraft instances to share them with anyone.
 * Support for every version of Minecraft that the vanilla launcher does, including snapshots.
 * Management of server and client text logs and in-game screenshots taken during gameplay.
 * Download mods and modpacks directly from within the launcher. The platforms currently supported are CurseForge, Modrinth, Technic, FTB and ATLauncher.