The best replacement for modbus is bacnet.

The best alternatives to modbus are rated as following:
★★★★★  bacnet
★★★★★  modbus plus
★★★★★  profibus
★★  rs485
★★  canbus
★★  fieldbus
★★  dnp3
★★  opc
★★  dnp
★  devicenet
★  modbus rtu
★  modbus tcp
★  ethernet ip
★  jbus
  dnp 3.0
  can bus
  lonworks
  hart
  tcp/ip
  ethernet/ip

Your alternative for modbus is not listed? Suggest!
Speaking about modbus, one probably shouldn't forget about rs485.

Other search terms related to modbus and their ratings are:
★★★★★ rs485
★★★★★ plc
★★★★ compactlogix
★★ micrologix 1400
micrologix 1100
You have in mind a companion for modbus and it is not yet here? Propose!



Google Trends

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modbus
bacnet
modbus plus