apkeep is a Rust command-line application for downloading Android APK packages from Google Play, F-Droid, and APKPure. It accepts single app IDs or CSV batch lists, optionally with version fields, lists available versions in plaintext or JSON, and downloads in parallel with configurable concurrency and sleep throttling. Google Play is the default source and uses the gpapi crate with OAuth/AAS/AUTH token flows, device profiles, split APKs, OBB additional files, and DexMetadata. F-Droid downloads are backed by cryptographically verified repository indexes (CMS/X.509 fingerprint and SHA-256 digests) with ETag caching; APKPure is deliberately gated behind an explicit danger-acknowledgment flag. Architecturally this is a modular async CLI: src/main.rs handles clap parsing, CSV parsing, ini config loading, and dispatch; each backend in src/download_sources exposes download_apps and list_versions and uses futures_util::buffer_unordered for bounded concurrency with indicatif progress bars. The code is readable and well separated, but it has no test suite, leans heavily on unwrap/process::exit for error handling, and repeats the three-retry download pattern in every source. The strongest engineering is in the F-Droid index verification and cache logic, which is non-obvious and hard to get right.