Postgres FDWs are extensions installed in Postgres. Multicorn provides an easy way to implement Postgres FDW extensions in Python, leading to many FDW implementations. Steampipe runs as a Postgres FDW extension with a pluggable interface to easily build and manage data sources. Multicorn-based FDWs might be installed as part of your existing Postgres server, while Steampipe is optimized to run more standalone / alongside your existing Postgres server.