What the Cepheus Engine actually is is a cleaned up version of the Mongoose Publishing version of Traveller 1st edition, which Mongoose had made available in SRD. Which we all know by now means 3rd party publishers could create compatible products using those rules.
Then Mongoose Publishing published Mongoose Traveller 2nd edition, discontinuing or changing the open license for 3rd party publishers. This made many publishers unhappy with Mongoose.
In response, either in frustration of the changed compatibility policies or with love for the system (or perhaps both), in July 2016 the Cepheus Engine rose up out of Samardan Press from Jason "Flynn" Kemp! The Cepheus Engine, which is the Traveller SRD, minus the Traveller setting.
Now, early into 2017, the system is hot! It appears almost all of the 3rd party publishers left behind with the 2nd edition Traveller rules are moving their aim to Cepheus Engine.
John Watts of Gypsy Knights Games shared this on G+...
Gypsy Knights Games has moved our entire Clement Sector line over to it and we've got lots of products in the pipeline as well as all of our existing material.John Watts also sent me to a sizable catalog of products already published at DriveThruRPG.
Zozer (Orbital, Star Trader) has moved their material over to it and are planning more.
Stellagama is working on a new setting as well as moving their existing material over.
Moontoad is working on materials for Cepheus Engine.
On top of that, there are other former Mongoose third party publishers who have migrated over to it. Indeed, I'd say 90% of them have done so. All of them are in the process of producing new material.
Add to that all of the new folks who are coming along to add their material. I know that Evyn is working on some new material. Michael Brown is producing all of his short adventures. There are more.
And, of course, Samardan is working on adding more to the line. The vehicles book is in process right now.
So The Cepheus Engine is here to stay and, frankly, I think it is the best thing going by far.
This is exciting!
It is interesting how I kind of struggled to be enthusiastic about Traveller 2nd edition, where enthusiasm for Cepheus Engine is far more genuine and feels right.
It is a little similar to what SciFi20 is to Traveller20.