ListenBrainz supports the Last.FM API and v1.2 of the AudioScrobbler API (used by clients like VLC and Spotify). Existing Last.FM clients can be pointed to the ListenBrainz proxy URL and they should submit listens to ListenBrainz instead of Last.FM.
Clients supporting the current Last.FM API (such as Audacious) should be able to submit listens to ListenBrainz after some configuration as instructed in the API Compatible README.
Clients supporting the old version of the AudioScrobbler API (such as VLC and Spotify) can be configured to work with ListenBrainz by making the client point to http://proxy.listenbrainz.org and using MusicBrainz ID as username and the LB auth token as password.
If the software you are using doesn't support changing where the client submits info (like Spotify), you can edit your /etc/hosts file as follows:
188.8.131.52 post.audioscrobbler.com 184.108.40.206 post2.audioscrobbler.com