Over the last 3 centuries, there have been numerous attempts to create an artificial, neutral international auxiliary language. the following is my attempt to list them:

in alphabetical order:
Esperanto
Glosa (AKA Interglosa)
Ido
Interlingua
Loglan (AKA lojban)
Neo
Novial
Occidental
Solresol (AKA soreso)
Volapük