It’s old news, but I was reminded about it recently. While Emacs has had support for rectangle operations (press C-x r C-h and look for commands with “rectangle” in their name) since a very long time, it acquired rectangle-mark-mode rather recently (a few years ago, in v24.4). It is a minor mode, switched on by C-x SPC, which temporarily (until the region is deactivated) highlights it as a rectangle, and changes the killing and yanking operations to their rectangle analogs. Also, C-x C-x in that mode behaves in a funny (though perfectly reasonable!) way. Of course, it doesn’t do anything that couldn’t be done earlier with rectangle commands, but you don’t need to remember so many keybindings anymore – just press C-x SPC and things like C-w or M-w Just Work™.