Bee email composer integration (alternative to Mosaico)
The mosiaco extension integrates the mosaico editor for mass e-mail editing in CiviCRM. However it is not an e-mail service.

I dont know of anyone in the community who have been looking into it, however there is a question on Stack Exchange about integrating a bee template into CiviCRM: CiviMail/Cron Fails using BeeFree template