The best bootstrapped SaaS of all time?

What would you say is the best bootstrapped SaaS of all time?

I would probably say it's kanuu.io but I'm probably a little bit biased there.

Since Kanuu works on Paddle, we did also just put together this list of some of our favourite SaaS companies that use Paddle - granted they're not all bootstrapped - but I'd be interested to hear what you made of our list.