The following can submit listens to ListenBrainz:

• Simple Last.fm Scrobbler, a scrobbler for Android devices: https://github.com/tgwizard/sls
• Last.fm Scrobbler, an extension for Firefox and Chrome: https://add0n.com/lastfm-scrobbler.html
• Lollypop, a modern music player for GNOME: https://wiki.gnome.org/Apps/Lollypop

It would be nice to add them to https://listenbrainz.org/api-docs