There are a few at companies that I've worked at. - Two previous companies have had hand-rolled timesheet tools (I'm sure there are plenty of alternatives now but both were probably built in the mid 2000s when there were't many alternatives) - A previous company had a integration environment booking tool - not sure why a custom solution was needed as any calendar tool should work but maybe there were some specific requirements (I was never a user of the tool) - A previous company had a tool for release management that pull in a bunch of items from Jira and marry them up with items in version control to generate a set of release notes in a specific format - no idea if there are any alternatives for this one but I think it had a pretty specific set of requirements None of the above would have been worth trying to monetise in my opinion.

There are lots of examples in the use cases section of any low-code vendor, but in short, most internal tools are not in the horizontal categories you listed. They're in vertical, industry-specific categories at SES (Software-Enabled Services) companies.

A quick commerce startup, for instance, is unlikely to find an inventory tracking app off-the-shelf that fits their workflow, since existing ERPs are not going to fit their workflow.

My company's got a handful of internal tools, but they're universally not useful to anybody else. We made a license creation tool that our manufacturing/sales teams use to make licenses for the hardware we sell, we have a stack of powershell scripts that create a bunch of required documentation from our bug tracker, and I made some custom tooling that made building our (nightmarish proprietary-language software) project easier to build.

build tools, often because they're so specific to the particular sw product

timesheet and similar types of tracking (often using Excel), again very specific to the particular org (it's more hassle to try to adapt some external tool)