The best replacement for web api is wcf.

The best alternatives to web api are rated as following:
★★★★★  wcf
★★★★★  mvc
★★★  wcf rest
★★★  servicestack
★★★  odata
★★★  mvc controller
★★★  wcf data services
★★  web api 2
★★  wcf performance
★  nancyfx
★  wcf service
★  mvc 4
★  asmx
  internet application
  asp.net mvc
  mvc 5

Your alternative for web api is not listed? Suggest!
Speaking about web api, one probably shouldn't forget about entity framework.

Other search terms related to web api and their ratings are:
★★★★★ entity framework
★★★★ mvc
★★★★ angularjs
★★★ web forms
★★★ authentication
★★★ windows authentication
★★★ mvc 4
★★ signalr
★★ odata
★★ asp.net web forms
★ mvc 3
★ basic authentication
You have in mind a companion for web api and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of web api in all years. Click on graph for more.
web api
wcf
mvc