The best replacement for ngui is daikon.

The best alternatives to ngui are rated as following:
★★★★★  daikon
★★★  scaleform
★★★  unity gui
★★★  2d toolkit
★★★  ezgui
★  daikon forge
★  uitoolkit
  igui

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

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



Google Trends

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ngui
daikon
scaleform