The best replacement for xamarin is phonegap.

The best alternatives to xamarin are rated as following:
★★★★★  phonegap
★★★★  mono
★★★★  xcode
★★★★  monodevelop
★★★  cordova
★★  telerik
★★  icenium
★★  sencha
★  robovm
  monotouch
  monogame
  objective c

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

Other search terms related to xamarin and their ratings are:
★★★★★ unity
★★★ genymotion
You have in mind a companion for xamarin and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of xamarin in all years. Click on graph for more.
xamarin
phonegap
mono