Now ESP8266Tone is implemented also as a b4xlib. Check the first post of the following thread:
Play tone in ESP8266.
Yesterday I tried to play a tone to a passive buzzer using the rTone library in a WeMos D1 Mini v3.0.0 module.. It was a complete fail because there is an inconsistency between Esp8266 boards and rTone library and B4R/Arduino reports that interrupt.h file is missing. So I figured a way around...