I suppose nobody really invents anything in-house in one sense. You reuse the hardware, the OS, the drivers, the network, cloud storage, IDE, source-control, JIRA, a programming language, several libraries, databases, at least one framework, and on top of all that you may have some sprinkles that are "your application."

I think the question is always, how smart an engineer can you be to reuse the maximal amount possible to deliver a good experience quickly.