Reddit, Fiverr, and DigitalOcean look undervalued relative to their growth potential.The tech sector is known for generating millionaire-making gains for patient investors. However, the world's top tech stocks -- like Nvidia, Microsoft, and Apple -- are already worth trillions of dollars and probably have less upside potential than the sector's smaller and lesser-known stocks.So today, I'll focus on three underappreciated small- and mid-cap stocks that could potentially deliver millionaire-making gains over ...