Meltano treats data integration like software development. A project defines extractors and loaders in a configuration file, and Meltano runs them to move data from sources into a warehouse. Because everything is code, pipelines live in Git, run in CI, and can be reviewed like other changes.
It builds on the Singer standard, which has hundreds of community connectors, and integrates with dbt for transformations and Airflow for orchestration. Teams can write custom connectors with a software development kit, which is handy for sources that commercial tools do not cover.
Meltano is free and open source. It requires engineering skill and maintenance, and connector quality varies. Alternatives include Airbyte, Fivetran, dlt, Dagster with integrations, and Singer itself. Meltano suits engineering-minded data teams.