La Folía is one of the oldest European musical themes. Several sources report that Jean-Baptiste Lully was the first composer to formalize the standard chord progression and melodic line, though it’s origins are probably much earlier. With a standard chord progression and common melody line, it has been the theme for many sets of variations and may have first developed as a compositional or improvisational method for creating melodies in the minor mode.

See a list of other free themes here.

Video:
Gunnar Idenstam – Improvisation on La Folia – Oscar´s Church, Stockholm, Sweden