link NFC Google API: http://developer.android.com/resources/samples/NFCDemo/index.html

link NFC Open API: http://www.open-nfc.org/opennfc_library/overview-summary.html
At the moment (Android 2.3.4), the Android platform does not integrate the Open NFC stack. This stack has several advantages: not limited to one particular NFC hardware, portable to many different environments (not only Android), many additional features compared to the current stack. On the other hand, because Open NFC is not part of the standard Android environment, it requires some work (but it is actually quite easy) to use this stack in an Android platform. The Open NFC documentation describes this process.

The Open NFC stack is parallel activity and is optional replacement to the current stack. Due to its description it overcomes some limits of the Google NFC stack implementation and makes new HW adaptions (i.e. support for new tag types) easier…

This stack is intended to by used by device manufacturers, not mobile developers, because the standard Android kernel does not support modules loading, the Open NFC stack cannot be simply installed as another application, it requires a kernel change. But once the kernel is replaced, it is quite easy to deploy and use the Open NFC stack. An application developer should probably stick to the OS features, even if more limited, since they assure the portability of the code over any NFC-enabled phone. But if you are trying to use "more" features than what comes with Android, Open NFC is a good candidate.

In Conclusion : Until some phone manufacturer will integrate the stack into device, it does not make too much sense to be interested in Open NFC stack. An app developer cannot make use of Open NFC unless it is on hardware.