The best replacement for google chat is skype.

The best alternatives to google chat are rated as following:
★★★★★  skype
★★★★  google talk
★  hangout
★  talk

Your alternative for google chat is not listed? Suggest!
Speaking about google chat, one probably shouldn't forget about lync.

Other search terms related to google chat and their ratings are:
★★★★★ lync
★★★★★ aim
sms
You have in mind a companion for google chat and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of google chat in all years. Click on graph for more.
google chat
skype
google talk