The best replacement for office 365 is google apps.

The best alternatives to office 365 are rated as following:
★★★★★  google apps
★★★★  office 2013
★★★  google docs
★★★  hyperoffice
★★★  office 2010
★★  exchange
★★  office for mac
★  exchange online
★  sharepoint
★  office 2011
★  office
★  outlook.com
★  sharepoint 2013
★  intermedia
★  exchange 2013
★  office online
★  office professional
★  bpos
★  hosted exchange
  outlook
  google apps for business
  gmail
  google
  on premise
  office 2007
  2013
  microsoft office 2013
  skydrive
  google drive
  office 2011 for mac
  live@edu
  exchange server
  google apps education
  google apps for education
  office home & student 2013
  office live
  windows live
  office student

Your alternative for office 365 is not listed? Suggest!
Speaking about office 365, one probably shouldn't forget about exchange.

Other search terms related to office 365 and their ratings are:
★★★★★ exchange
★★★★ outlook
★★★★ sharepoint
★★★ visio
★★ adfs
★★ outlook 2007
★★ office 2010
★★ autodiscover
★★ outlook 2003
★★ tls
★ microsoft account
★ outlook 2013
★ office 2007
★ access
★ active directory
★ mac mail
skydrive
imap
sharepoint what version
lync
exchange 2010
You have in mind a companion for office 365 and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of office 365 in all years. Click on graph for more.
office 365
google apps
office 2013