There is one other file type using
the ETA file extension!
.eta - Keyhole EarthViewer placemark or overlay data
ETA file extension - eTreppid audio file
What is eta file? How to open eta files?
File type specification:
The ETA file extension is used for eTreppid audio file (eTplayer and ETVC media CODEC).
Probably older and no longer supported auido file format.