For me it was Enlightenment DR16 (discontinued). you could make themes with shaped borders (transparent regions, buttons and titles anywhere, even overlapping into the window a bit), have it remember window positions, change border style for a window (e.g. drawer, so it can be collapsed sideways) and it would not steal focus. it had really good effects and features. I miss it a lot in Wayland. Check the web for some screenshots, if you want to be inspired.