What is the difference between NGFB and WPSSO Core?

The WPSSO Core plugin is a fork / child of NextGEN Facebook (NGFB) — they have the same author, the same solid core features and code-base, but WPSSO Core is distributed without the social share buttons and their related features. Additional Free extension plugins are also available for WPSSO Core, including two different types of sharing button extensions:

If you wish, you can add the same social sharing button features to WPSSO Core using the WPSSO SSB extension plugin (both Free and Pro versions of the WPSSO SSB plugin are available). The combination of WPSSO Core and WPSSO SSB is functionally equivalent to NGFB.