I love that jeelabs blog.. Also, some languages running on esp8266:

https://github.com/yesco/esp-lisp

https://github.com/zeroflag/punyforth

https://micropython.org/

(and of course lua which i didn't try because its official... https://github.com/nodemcu/nodemcu-firmware)

damn that looks fun. as if I didn't already have enough things I want to learn...