Prototypr Weekly newsletter has been running for a few years now, and the project is sustainable through sponsorships.
At the same time, I've been building another product, "Letter", an email creator for designers. This is the tool I actually use to build the Prototypr newsletter.
Funnily, this week, instead of getting a sponsor, I added a Letter banner as the sponsor slot, and had 20 new signups (+ around 80 clicks so far) ...from my own newsletter, built with the tool that is appearing as the sponsor.
Lesson is, if you make multiple products, see if you can connect them to grow from eachother. Once Letter is launched, maybe it can be a regular paying Prototypr sponsor.