macOS. There's no Alt+Tab, for example: no way to switch between two arbitrary windows on the Z-stack¹. The not-equivalent that exists is ⌘+Tab, and it switches apps; the usability of it, vs. Alt+Tab, is horrendous. (It fronts stuff you don't want, covering up stuff you do want.)
There are workspaces … but I have found them hard to get productive with: macOS will reorder keystrokes around workspace changes. That is, the keyboard input "abc ^→ (workspace change) def" is a race condition: typed quickly (within the animation delay), it becomes as if you typed "abcdef ^→".
¹no, ⌘+` does not count.