Here is a Youtube video from The Race Club head coach 3 time US Olympian Gary Hall Sr who was also a World Record holder in the 200m Butterfly providing a brief overview of the two foundational forms of the Freestyle stroke and one derivative form of the stroke:
– Freestyle with a Hip driven stroke (foundational);
– Freestyle with a Shoulder driven stroke (foundational);
– Freestyle with an alternating Hip – Shoulder driven stroke (derivative).
Note: video is dated Feb 2011, so none of this is brand spanking new technique, in fact, Freestyle technique has evolved since this video.