In SaaS, the stand-out example may be Mailchimp.
Mailchimp is now approaching $1 billion in ARR and is 100% bootstrapped. And it started off as a true side project:
“Mailchimp, named after their most popular e-card character, launched in 2001 and remained a side project for several years, earning a few thousand dollars a month. Then in 2007, when it hit 10,000 users, the two decided to commit full-time”: The New Atlanta Billionaires Behind An Unlikely Tech Unicorn
This story is a good reminder that bootstrapping has its rewards. The founders of Atlassian and Mailchimp in SaaS will own the most, and probably make the most.
But boy it often takes longer. Mailchimp took 6 years to get to enough critical mass the founders could go full-time