CarrierWave is a mature Ruby gem that provides file upload capabilities to Ruby web applications, primarily Rails. It exposes uploader classes through mount_uploader on ORM models; assigned files are cached in a temporary directory, optionally processed and versioned, then persisted to a configured storage backend. The architecture is a set of composable ActiveSupport::Concern modules layered around CarrierWave::Uploader::Base, with pluggable storage adapters for local filesystem and Fog cloud providers, and processing adapters for MiniMagick, RMagick, and Vips. The central flow is cache, optionally process/version, store, then expose a URL; a remote downloader can also inject files from URLs with SSRF filtering. Production behavior is backed by a large RSpec suite and Cucumber features. It supports single and multiple uploads, metadata columns, direct-to-cloud uploads, cache cleanup, and ActiveRecord callbacks including after_commit deletion and rollback handling. External dependencies are limited to ActiveSupport/ActiveModel, Marcel for MIME detection, ssrf_filter for download safety, and optional Fog/image processor gems. This is not a standalone application or service; it is embedded into host applications as a library dependency. Maintenance is active, with ongoing 4.0.0.rc development and a Rails version matrix. Technical drift is moderate: the codebase still supports Ruby 2.7, contains a permissive RuboCop configuration, legacy scripts, and several deprecation layers, but the core abstractions are current and extensively tested.