The best replacement for open system is closed system.

The best alternatives to open system are rated as following:
★★★★★  closed system
★★★★  shared key
★  mainframe
★  closed
★  shared key authentication
★  close system
★  share key
★  shared
  shared key wep
  proprietary system

Your alternative for open system is not listed? Suggest!
Speaking about open system, one probably shouldn't forget about closed system.

Other search terms related to open system and their ratings are:
★★★★★ closed system
You have in mind a companion for open system and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of open system in all years. Click on graph for more.
open system
closed system
shared key