Other sites where friends describe their projects:

Romek Kubat's blog (in Polish)
Cezarowy Blog (in Polish)

IoT projects:

ESPEasy 2.0 – installable versions (binary)
– Gijs Noorlander Projects

SMOG, air quality and purification:

SMOG measurement project on ESP8266 – all in one, various devices – Air Quality from Jan Szumiec
Do-it-yourself – air purifier
Advanced design with ESP8266, smog sensor and heating (enc-X)
Jack's project - better charts for SMOG, here is the blog

SMOG/meteo stations:

Łukasz Trąbiński and his station METEO.