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 add-ons are also available for WPSSO Core, including two different types of share button add-ons:

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