I find it really weird that IMGUI has a DragWindow function but not a ResizeWindow function. It would be really nice to be able to resize windows. This feature seems to be on Unity's radar to some extent, as in the UI Samples asset made by Unity, there is a script that allows UI to be resized via dragging on a specified UI image/rect. It would make sense to have a similar feature for IMGUI. I've seen forums about how to accomplish this, but they're a bit hacky and don't really work so please Unity, add this feature.