Good Energy uses Octopus' systems both IT and customers service, but have different sources of energy, and also seem to insruct Meter Asset Providers in way that may be quicker than Octopus and offer for example three-phase meters quicker. They remove meters and cap gas supplies for free, like Octopus. It markets itself as an environmentally friendly: Good Energy (orginally Unit-E). With them you pay slightly more than price cap as allowed due to OfGEM assessing that they provide the green value over companies subject to the price cap.
Related links being added including electricification of heat below.