No, unfortunately I don’t know of any native GTK App that achieved this on Kindle. The standard Kindle framework runs in (some ancient) Java, and accessing that framework and its features is not well documented at all.
What could be done without much effort is to implement a context menu, that opens when you do a “touch & hold” gesture, like kterm implements it, screenshot: http://www.fabiszewski.net/kindle-terminal/ (kterm = terminal emulator for Kindle).
KOReader for Kindle has something similar to the Kindle’s top-menu, but it is an implementation they did themselves, and they use a different programming language and possibly GUI framework.
I was rather focusing on things that could be done easily, and that enhance my personal usability experience, so I focused on “glueing” touch gestures offered by the used Xorg touch driver to already existing gargoyle functions. Without that, I found editing the input line to be a pain, because the Kindle’s on-screen keyboard lacks any ctrl-keys and cursor keys, nor does the GUI framework support exact touch based cursor positioning (like the magnifying glass in iOS).
What I was also looking into, but didn’t find any info about (yet), is this:
mobileread.com/forums/showt … p?t=283918
I would like to use this for word suggestions, but the on-screen keyboard’s API is not open (as could be expected).
Still, I am now quite happy for my personal use. Next step would be to clean up the implementation to be able to send a pull request to the main gargoyle project. Only after that would I look into more features.