1. In single file
   "the prisoners came out one by one"
   - one after another, one at a time 
2. One piece at a time
   - by the piece 
3. Apart from others
   - individually, separately, singly, severally, on an individual basis

Encyclopedia: One by one

• low-keyed
• low-level
• low-level formatting
• low-level radioactive waste
• low-lying
• low-minded
• low-necked
• low-pass filter
• low-pitched
• low-powered
• low-pressure
• low-priced
• low-resolution
• low-rise
• low-salt diet
• low-sodium diet
• low-spirited
• low-spiritedness
• low-sudsing
• low-tech
• low-tension
• low-toned
• low-voltage
• low-warp-loom
• low-water mark