The Common Era Calendar is a concept invented by Peter Meyer. It is the same as the Gregorian calendar but applies with the same rules to days before its adoption like the Proleptic Gregorian calendar and uses astronomical year numbering with the Common Era.
The calendar gets its name from the fact that Common Era (CE) is always used in the year number, even for years before 1 CE; e.g. -44 CE for 45 BC or 45 BCE.
You will see its use in text originally written by Peter Meyer, for example in Goddess Lunar Calendar.