Fisher is a pure-Fish plugin manager for the Fish shell. It provides a CLI with commands to install, update, remove, and list plugins, which can be sourced from local directories or remote tarballs (GitHub or GitLab). The entire implementation resides in a single `fisher.fish` function (~250 lines) that handles argument parsing, concurrent downloads, file placement, event emission, and state persistence via a `fish_plugins` file. The architecture is monolithic but well-structured, using Fish-specific features like universal variables and event hooks. No external dependencies beyond curl and tar are required, and the tool is designed to be zero-configuration and snappy. The test suite uses the Fishtape framework with a sample plugin (ponyo) to validate install/update/remove flows and event handling.