I recently did a breakdown of how Replit went from a side project to $800M company. A few things stood out to me about growth:
Amjad Masad, the co-founder and CEO, firmly believes that people are willing to try new products. If your product is good, then posting relentlessly on HackerNews, Reddit, Twitter, etc will pay off
The HackerNews launch in 2011 remained one of Amjad's most popular posts. It drove a lot of traffic early and the co-founders of Codeacademy ended up discovering the open-source project shortly after. Paul Graham discovered Replit through HN and they ended up going through YC W18 7 years after the original post
Replit had built-in virality for the next generation. They sold schools and teachers. Each time a teacher used Replit, it immediately adds 100+ students. They eventually develop a habit of only using Replit.
Engineering Growth by focusing on building features that incentivize people to share. Bounties are a great way to do this. You get the community-building necessary features, and people who make money doing so want to share the latest side hustle they found.
Hope this all helps you!