Utilities & Energy Portals (Unofficial Web/App API Clients): open-source projects that exist because someone reverse engineered a closed product, sorted by GitHub stars.
EPEX Spot electricity prices, including sources found by reverse engineering supplier websites
China Southern Power Grid usage statistics via the CSG mobile app API
Wiener Netze smart meter readings via the unofficial smart-meter portal API
Israel Electric Corporation consumption and invoices via the unofficial IEC app API
Hydro-Québec consumption and peak events via the unofficial customer portal API
Inter RAO utility personal-account data (Russia) via the unofficial web API
Aigües de Barcelona water usage via the unofficial customer portal API
EyeOnWater water meter readings via the unofficial EyeOnWater web API
Oma Helen electricity consumption (Finland) via the unofficial customer portal API
PGNiG gas usage (Poland) scraped from the eBOK customer portal
Greenely energy usage and prices via the unofficial Greenely app API
Belgian Fluvius smart-meter data pulled from the Mijn Fluvius portal API
Greenchoice energy usage (Netherlands) via the unofficial Greenchoice API
Ecojoko energy assistant data via the unofficial Ecojoko API
ista EcoTrend heating and water consumption via the unofficial ista API
Geo Home smart-meter display data via the unofficial Geo cloud API
Total Energies Key Atome Linky live consumption via the unofficial Atome API
Energa Mój Licznik electricity data (Poland) scraped from the customer portal
Veolia water consumption (France) via the unofficial customer portal API
Electric Ireland Insights consumption data via the customer portal
Unofficial Python library for the Portland General Electric customer API
Unofficial Python client for the Green Mountain Power API
Reverse-engineered EDF (French electricity) customer API client for JavaScript
Unofficial client for the GRDF gas meter consumption API