Excel, SAP, AutoCAD, Photoshop, and many many others. All require quite a bit of training even if you already know similar software.

I learned excel and photoshop on my own, without documentation, just figuring things out as needed. Asking someone "do you know how to refer to the value in another cell?" is not the same as reading documentation. Both SAP and Autocad are super domain specific, and likely used by far fewer than 1% of computer users.