Your reply shows exactly why a thread is needed!
erskyTx is an open source firmware for transmitters (it is shipped as an option on the FrSky X9Lite). It is NOT obscure, indeed many users prefer it to openTx.
History:
The 9X transmitter had TH9X written for it, that was then developed as er9x. open9X was forked from er9x. The SKY upgrade board, with an Atmel ARM processor was produced for the 9X. ersky9x was then created for this, and openTx was created to support the ARM processor as well. As other radios became available I renamed ersky9x to erskyTx.
The 9XR-PRO was a HobbyKing product that used a main board developed from the SKY board, and shipped with ersky9x installed.
erskyTx runs on nearly all FrSky radios as well as other makes.
It does support the efforts of Aloft. I have seen new users give up on a FrSky radio because they don't "get on" with openTx. These users may well find erskyTx more suitable as it is easier to use then openTx, while still having all the power of things like "everything is a mix".
Some new features in openTx actually appear in erskyTx first, e.g. the reporting of the RTC battery voltage.
Some example displays of erskyTx (QX7):
Mike