Blue Reverie is a fanmade expansion created by discord user Tactic Blue, the same user who organized the Discordant Stars expansion. It currently consists of 6 new factions (with 3 more planned in the future), along with a mix of new and reworked content involving technologies, agendas, relics, and promissory notes. The expansion is still in development, and should be expected to change as time goes on.
The public reference document for this expansion can be found here.