To earn $100 without any investment, explore online freelancing platforms like Upwork or Fiverr, offering services such as writing, graphic design, or virtual assistance. Utilize your existing skills to provide valuable services to clients. Additionally, participate in online surveys, sign up for affiliate marketing programs, or sell unused items on platforms like Craigslist or Facebook Marketplace. Engaging in these opportunities can help you reach your $100 goal without any initial investment.