(If you haven't read the high level overview, Simple x "Never" = Insane, you might want to start there.)
A collaboration tool between Eng and Ops
Some tools exclusively focus on the engineer (React, Retool, Jupyter Notebooks, Postman, Swagger UI, Pipedream, Autocode). Other tools focus exclusively on Ops (Zapier, IFTTT, Integromat, Appian). Very few tools start with the premise that Eng and Ops are working on this problem together. Realistically, the engineer needs to write some code. And the Ops person needs guardrails. You can't let Ops terrorize a production database. But the engineer doesn't have to do everything. Ops can do the bulk of the work. And they should, too, because they're the end users.
The UI of an "internal tools" typically consists of a few form input fields with a "Submit" button and some guardrails. That UI should be automatically generated. It's not worth anyone's time to build it. Swagger UI is the closest example, but most apps are being built in React or Retool, where the UI has to be made to match a decoupled backend. Yes, autogenerated UI sacrifices customizability, but that's the point -- the existing tools optimize for customizability, and nothing optimizes for speed. In some ways, autogenerated UI is as much an extension of CI/CD as it is a precursor to custom app development.
Programs built incrementally, mostly by Ops
Run a query, play around with the data, pipe it into another API request, oops undo that, pipe it into a different API request. Engineers know this feeling, but I'm not sure that Ops people have felt this yet. Most low-code tools make you lay out every step, then cross your fingers and hope the whole thing works. Instead, it should feel like a REPL or a Jupyter Notebook.
Private-cloud first, SaaS second
What types of companies build internal tools? Marketplaces, Logistics, Payments, and Healthcare. There's a lot of overlap between those verticals and the set of companies handling personal identifiable information (PII). Those companies prefer to private cloud deployments, to avoid any risk that a 3rd party SaaS product mishandles their PII. Zapier, IFTTT, and Integromat are great for connecting low-stakes 3rd party tools (e.g. Gmail -> Dropbox), but they aren't designed for connecting internal APIs in your private cloud.
Breezy, dare I say fun?
The other day I claimed that using Notion is fun, which made Bryce and Mallory squint with an obvious look of "that's what you consider fun?" So I backtracked and went with "breezy." But I have to say, tools that are super breezy verge on fun.
What does "breezy" mean in this context? I think it means perfecting the boring, low-level operations. Why does Notion feel breezy? It's because they've perfected the most boring little operations. Things like: write one sentence, hit enter, start a bullet list. It adds up. Most app-building platforms (e.g. Appian) focus way too much on complicated stuff -- we need a canvas that allows Ops people to build DAGs with 50 nodes. The complicated stuff isn't what slows people down though. (Most internal tools are simple.) What slows people down are little points of friction in the most basic operations. What's needed is an insane attention to detail for basic operations like, "how do I convert this JSON output to a table?"
A spreadsheet lover, not a "spreadsheet killer"
A corollary to the previous point. Ops Land is all about Excel. And that ain't changing. Workflows like this are common: to run payroll, run a query, download to Excel, manually add promos, upload CSV to payroll tool. A lot of tools like to market themselves as spreadsheet killers, but what's really needed are tools that eliminate the friction to and from spreadsheets.