Como quase todo mundo sempre achei que o “beta” de versão beta vinha da letra grega “ß”, mas aparentemente ele vem do trocadilho “BETA than nothing” conforme Guy Kawasaki no livro The Macintosh Way e a expressão alpha vem muito depois quando os programadores já adotavam a expressão ß.

The term beta is an abbreviation of the phrase beta than nothing, which is exactly what beta software is. Software companies like to give beta sites beta software because they think it prevents them from buying the shipping versions of their competitor’s products. When a company tells you a ship date for beta software, you’d better be able to read between the lines.

Guy Kawasaki, The Macintosh Way