I developed this extension for a client.
But ultimately he didn't like it.
Hope it could come useful to at least someone.
I've tested this extension with prosilver style only.
But it should work with other styles as well.
Feel free to provide feedback and let me know if I should add/change any functionality to it.
Also comment if this extension doesn't work with your style.
Description:
This extensions adds a Mega menu / sticky menu to your phpBB forum and lets you customize it through ACP.
Normal menu items can be added and edited through ACP.
Knowledge on twiiter-botstrap is required for mega menu implemetation. Sample menu item has been added as example.
Screenshots:
Dropdown Menu:

Mega Menu 1:

Mega Menu 2:

ACP:


Installation:
Upload orthohin directory to your board's ext directory.
Enable the extension in ACP.
Resources Used:
Isolated Bootstrap
Yamm 3!
tinyColorPicker
placeholder.com
Download on github:
https://github.com/orthohincom/phpbb-navbar
Version 1.0.2
Changelog:
-> Added support for template variables in html field.
Version: 1.0.1
changelog:
-> fixed an sql error while editing sub-menu item.
-> fixed an issue where text inside the dropdown box are bigger than the dropdown box itself.
To-Do:
[*] Enable Language Variable support in MEGA HTML field.
[ ] Enable use of IF statements in MEGA HTML field.