WordNet sense 1 (someone who enlists workers to join a union):

organiser, labor organizer

WordNet sense 2 (a person who brings order and organization to an enterprise):

arranger

WordNet sense 3 (a lightweight consumer electronic device that looks like a hand-held computer but instead performs specific tasks; can serve as a diary or a personal database or a telephone or an alarm clock etc.):

PDA, personal digital assistant, personal organiser, personal organizer