It's an extension for github.com/cli/cli that adds some stuff for managing git worktrees.

commands to create and manage git worktrees

Usage:
  worktree [flags]
  worktree [command]

Available Commands:
  completion  Generate the autocompletion script for the specified shell
  help        Help about any command
  pr          worktree from PR

Flags:
  -h, --help   help for worktree

Use "worktree [command] --help" for more information about a command.