The answer is certainly Microsoft Teams but since there's already a large section on that, I'll say Visual Studio. VS is largely a wonderful piece of software

The answer is certainly Microsoft Teams but since there's already a large section on that, I'll say Visual Studio. VS is largely a wonderful piece of software but sometimes just stops working in inexplicable ways. Sometimes I have to build 5 times without changing anything to get it to succeed. Sometimes my build fails but the only error in the error list is about projects that couldn't be loaded (because they failed to compile for some mystery reason). Sometimes it just randomly freezes doing basic tasks. My recent favorite is this endless string of banner errors at the top of the screen saying that there's an error with my projects that I can't dismiss or hide. VS is great, but also sometimes the worst.