The best replacement for packet tracer is gns3.

The best alternatives to packet tracer are rated as following:
★★★★★  gns3
★★★★★  boson
★★  boson netsim
★  network simulator
★  wireshark
★  opnet
  netsim
  dynamips

Your alternative for packet tracer is not listed? Suggest!
Speaking about packet tracer, one probably shouldn't forget about wireshark.

Other search terms related to packet tracer and their ratings are:
★★★★★ wireshark
★ sdm
You have in mind a companion for packet tracer and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of packet tracer in all years. Click on graph for more.
packet tracer
gns3
boson