Where I work we use a combination of lightly customized tools out of the box (Jira, Jenkins, ...) as well as full custom applications such as the editor that our data team uses to maintain our database which is a React app like our customer-facing app.
I also have a number of personal tools such as a Python program that (most of the time) can automatically merge changes to the maven and npm projects I work on, apply liquibase changes to the database and build and test everything plus keep track of branches and stuff so I can sync up most mornings and not have to think about and not make silly mistakes with git and pull requests.
I've worked at places where it took 20 seconds for JIRA to load the page for creating a new ticket but I'm 100% delighted with our JIRA installation. I might have complained about tooling before I built my "maintenance droid" but now I won't. I know the data team and marketing people like our editor (e.g. they use it to manage customer subscriptions)
With control over our internal systems it's easy for us to innovate. For instance we are developing generative AI tools that work together with our data team to speed up OCRing data on paper and getting it up to our standards. You can use all kind of API integrations with prebuilt tools, for instance I use ticket numbers all the time when I discuss my work in Slack and it's not hard to write a program that looks at a year of standup messages in Slack and what is in JIRA to write the beginnings of my performance review.
What I'm not getting about retool is this: it looks like a "low code" or "no code" platform that is intended for internal tools, what stops you from using the same tool for both internal and customer facing applications?