Using a single CAT5 wire to terminate 2 data jacks. Since the Orange and Green pairs are only used in a CAT5 cable (not counting PoE or 10/100/1000 installs) the blue and brown pairs are not used, so they can be used to connect as a second "orange" and "green" pair on a second jack (as long as you terminate them both the same way on both ends of the cable). This should be avoided whenever possible, but can help to bring a second CAT5 jack somewhere that would be nearly impossible to pull a
This one is a little bit more creative. I needed to install push buttons for 3 door releases. My company did not want me pulling new runs. There was a CAT5 run near where the buttons needed to go to, but the fax line was connected to it. I installed a 8p8c connector terminated normally (568B) and split off the blue/white pair to a surface mount jack to connect the fax machine to. The remaining 3 pairs each went to a separate door release button. If needed to add more, I could have used a common wire for each button, to increase the amount of push buttons to a maximum of 5 + the fax dial tone. (or 7 if I did not need to have the dial tone working there.) Best thing about this installation, it is easily removable - or its concept can be used for other temporary applications using existing CAT5 wiring.