Unfortunately none. The NDK is much more complicated to write with as it allows for full C++ code interacting directly with the hardware without the Mojo abstraction layer. Using it for non-graphically intensive applications would be overkill for the average WebOS developer.

FYI: Mojo was originally intended to allow WebOS applications to be written much the same way as interactive web pages to ease development, unlike the complicated C++ application languages used by more complicated apps (games and traditional programs).

This is the main reason why WebOS was called WEB OS as it was supposed to be just as easy to write apps as it was to write web pages.

However, when the iPhone started making waves with more complicated games running in standard code and producing performance and visual effects outside the range of Mojo ( or in the case of Android's Java based abstraction layer: Dalvik) then Palm released an NDK allowing the same complicated and graphically intense code to execute on WebOS. If you look, Google released an NDK that bypasses Dalvik around the same time.