iOS' Quick Reply feature on WhatsApp for Android
Android N will have native quick reply feature (called Direct Reply), and while WhatsApp will probably use it, it won't work for pre-N (although it has implemented its own quick reply from notification for all Android version).

However, there are some apps that can emulate the direct reply feature on Android N:


quickReply (free, 5.0+)


  quickReply will show you separate notifications for every contact including reply action buttons, so you can easily write quick replies without opening the messaging app.
  
  QUICKREPLY SUPPORTED APPS:
  WhatsApp, Telegram, Threema, Skype, Line, WeChat, Kik, EvolveSms, YAATA, Textra, ChompSms, Hangouts, Handcent SMS... 

Floatify - Quick Replies (free, 4.3+)


  Advanced heads-Up notifications for your phone! QuickReply lets you send messages directly from the notification! ...
  
  MAIN FEATURES:
  Heads-up Quick Replies (5.0+, limited on 4.3+, see below for supported apps)
  
  QUICKREPLY REPORTED WORKING:
  WhatsApp, Telegram, Threema, Skype, Line, WeChat, Kik, EvolveSms, YAATA, Textra, ChompSms, Hangouts, Handcent SMS... 



Both apps are developed by Jawomo, so it's not really surprising they have similar feature and supported apps...