Paid In Bio https://www.paidinbio.com
HN is probably not the target audience for this, but I've become really obsessed about solving my own problem of building apps, but struggling to market them. There are very few places online that welcome you to post links, enable you to post a link quickly, and drive targeted traffic at reasonable cost.
So I'm trying to bootstrap a new ad network on Link In Bio platforms that offers this trifecta (welcoming, quick, cost effective).