At JetBrains, we use a single TeamCity installation to build all of our products – including the giants like IntelliJ IDEA, PyCharm, Kotlin, as well as hundreds of plugins, and a lot of internal products and services, such as the website or this blog.
In total, it amounts to 7,500 projects, 50,000+ build configurations (jobs), and around 65,000 builds per day on average. This is all handled by 2000+ build agents (although this number is not static as a lot of them are launched on demand and run builds in hosted environments, such as AWS).
All of that is handled by our internal CI/CD server