Generate a full detail guide on 'Impact Investing.' The guide should be for investors and socially-conscious entrepreneurs. It must include detailed sections on: 1. A clear definition of impact investing and how it differs from charity or traditional investing. 2. A breakdown of the different sectors where impact investing is common (e.g., renewable energy, affordable healthcare). 3. A guide on how to measure social and environmental impact (e.g., ESG metrics). 4. A list of platforms and funds that specialize in impact investing. Please include a disclaimer that this is a complex investment class requiring due diligence.