There are several different pitch-shifting or vocorder plugins available. The most famous, and perhaps the most widely used by professionals, is Antares Autotune. The unique, slightly robotic singing voice sound you can produce with Autotune first became famous in Cher's hit Believe, in 1999. More recently, Autotune has been used extensively in songs by the rapper T-Pain.
Autotune isn't free, but there's a free alternative called GSnap.
These programs can also be used to correct the pitch of a vocal that is slightly out of key and Autotune is often used in commercial songs to avoid having to do another take when a small part of vocal isn't perfect the first time around.
To use them in Mixcraft, place the DLL in C:\Program Files\VST\ or go into Mixcraft's Effects preferences and add the plugin's folder to the list of VST folders Mixcraft is searching.
Note: there are Youtube videos on how to tweak these plugins to get the sound you want.