https://npsbeacon.com NPS survey and analysis tool. I built this because I needed an easy and cost effective way to manage NPS surveys and almost had a heart attack when I learned what some of the competitors are charging.
https://contributoriq.com/ Helps tremendously with the M&A process during due diligence when you need to quickly understand who are the SMEs in specific parts of code base.
https://dependencydesk.com Another M&A tool. Useful for software company sellers who are required to disclose details related to software IP ownership such as what third-party dependencies are used in their software.
https://securitybot.dev All-in-one security, uptime, and SEO monitoring tool. I love working on this, and it has been so useful helping to identify various issues in my other products. Simple Slack alerting integration.
https://iterops.com Heatmap, rage click, dead click, simple A/B testing tool. Like NPSBeacon I built IterOps because the competing solutions are charging far too much for what they offer.
https://spiesindc.com One of these projects is not like the other lol. This is that project. Cold War history / stamp collecting subscription service. I probably lose money on this and yet will never stop running it.
My personal rule is to only build side projects that I plan on using all the time. Otherwise I'll just lose interest and they will languish. So far, so good.