This stuff is called "wire-wrap wire" because it used to be used for wire-wrapping high-speed digital circuits on a special kind of contact board. It's pretty rare to see wire-wrapping in these days of low-cost PCB fabrication but the wire is still really handy for prototyping work. It's extremely thin (30 AWG!) so your wiring won't get bulky, and it is just stiff enough to hold its shape around corners. It's most commonly used for SMT rework ('oh man, i swapped two pads') or repair ('ok let's bridge this via to that via to fix a broken trace') but it's also great when you need to get a signal from here to there through a small space.