If you haven't seen it all the weapons in RWBY all have several modes they can near instantly shift between. These mods can give the weapon new abilities, change the way it functions, or more commonly change it into an intierly different weapon.
See bellow for examples...some are from the show some are fan made:
https://www.google.com/search?...__TeyAIVAck-Ch0X-w9o
So share, what ones do you like the most, and what ones have you come up with yourself?