It's the Pied Piper, Charlie Brown is the last animated special produced under the supervision of Charles M. Schulz. Based on characters from the comic stripPeanuts, it was released on September 12, 2000, seven months after the death of Charles Schulz. It has yet to air on TV. It's The Pied Piper also has the distinction of being the first new Peanuts special to be released to DVD.
It's the Pied Piper, Charlie Brown is a retelling to Sally by Charlie Brown of the story how the Pied Piper of Hamelin (portrayed by Snoopy) chased away all the mice (changed by Charlie Brown from rats because, upon the story saying that the rats fought the dogs and killed the cats, Sally is terrified of rats) from the town of Hamlet. The Peanuts kids substitute some characters, Snoopy being the Pied Piper Beagle with his contract being for a year's supply of dog food. Snoopy plays a concertina (squeezebox, with presumably David Benoit doing the honors). The special breaks Peanuts tradition in that it shows adults, who speak audible language (unlike most other Peanuts specials in which adults are only heard off stage speaking in "wah wah" sound of a muted trombone). The other good example was the This is America, Charlie Brown miniseries, which portrayed adult historical figures alongside the kids.