Well, I've spoken about this before, and on here no less, but only really in response to posts like this. I don't do any advertising or speak about mine except in interviews, since it's usually indicative of the kind of requirements they're looking for.
I created a SaaS bootstrap for Javascript called Nodewood [1]. It actually started as just a template for me, because there's a lot of setup for each new JS web project that I kept skipping to get to the "fun" stuff, like I'd just hard-coded the user as ID #1 instead of writing user registration/login code. Since then, it's grown to also have form validation, a starter UI, teams support, subscription support with Stripe, an admin panel, a CLI tool, and I'm currently adding a deploy option via Pulumi [2].
I've sold a few licenses, but also it offers me a platform to "scratch my own itches", which then become available to the people who bought a license.
[1] - Nodewood: https://nodewood.com
[2] - Pulumi: https://www.pulumi.com/