ANSWER
Solresol, or "La Langue Musicale Universelle", is an artificial language, and was intended to be an interlanguage - a common second language to allow communication among different people from around the world. Over the years, a number of artificial interlanguages have been developed, most notably Esperanto, but Solresol is different from other artificial interlanguages in two important aspects.
First, it was the first artificial language to be taken seriously. It was developed by Jean Francois Sudre, who first demonstrated it to the public in 1833, having already completed Solresol dictionaries in seven languages. After his death in 1864, his language continued to grow in popularity, reaching its peak in 1902 with the publication of "Grammaire du Solresol", by Boleslas Gajewski. After that it quickly faded into obscurity, eclipsed by Esperanto, which was decidedly easier to learn for the average European.
The second thing that sets Solresol apart from other artificial languages is the unique nature of the language, which allows it to be easily communicated using a variety of non-verbal methods. Every word in Solresol is composed of a combination of seven syllables, DO, RE, MI, FA, SOL, LA, and SI, which correspond to the seven notes of the musical scale. (In case you are wondering about that last syllable/note, it was "si" in the 19th century, today it is "ti", a drink with jam and bread.)
Thus a sentence could be spoken, or played on a musical instrument. The seven syllables could also be represented by the seven colors of the rainbow (red, orange, yellow, green, blue, indigo, violet), so a sentence could be expressed with nothing more than a series of colors. Sudre also devised a system of tapping on one of seven positions on a person's palm to enable communication among the blind and the deaf. (A novel idea for the 19th century.)
Of course, having musical notes "speak" could cause some unintended consequences. Greg Baker, a modern day Solresol enthusiast, said he found himself wondering why "the beginning of Beethoven's Fifth seems to talk about Wednesday".
For more information: An interesting history of Sudre, and the development of Solresol was written by Paul Collins for Fortean Times magazine. The article is available online at http://www.forteantimes.com/articles/145_solresol.shtml
WHO GOT IT RIGHT: Kathi Reynolds, Scott Flaxman, Cindi Lou, Robert Walker, Arne Haaning, Robin Campbell, Marika Thiessen, Trish Boggs, Bob Milligan, JP Weigt, Marc Quinlivan, Gregory Combs, Alan O'Keefe, Demon Kitty, Ilana G, and Richard McGrath.
