A number of features or background services communicate with Google servers despite the absence of an associated Google account or compiled-in Google API keys. Furthermore, the normal build process for Chromium involves running Google’s own high-level commands that invoke many scripts and utilities, some of which download and use pre-built binaries provided by Google. Even the final build output includes some pre-built binaries. Fortunately, the source code is available for everything.
ungoogled-chromium tries to fix these things.