The best replacement for io is iv.

The best alternatives to io are rated as following:
★★★★★  iv
★★★★  outboard
★★★  second city
★★  iox
★★  nio
★  io
★  ia ntu
★  ob
★  reef crystals
★  ucb
  inboard
  ia
  smorph
  lynx aurora
  dm5
  io mapped io
  nio java
  cached io
  europa
  bone injector gun

Your alternative for io is not listed? Suggest!
Speaking about io, one probably shouldn't forget about control logix.

Other search terms related to io and their ratings are:
★★★★★ control logix
★★★ dd
★★★ controllogix
You have in mind a companion for io and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of io in all years. Click on graph for more.
io
iv
outboard