X(3), X(4), X(5), X(52), X(68), X(155), E(593)
feet of altitudes and their reflections in X(5) (these points on the perpendicular bisectors)
reflections of A, B, C in X(5) : centers of circles HBC, HCA, HAB i.e. centers of the Johnson circles
It is the locus of point M such that the parallels at M to AO, BO, CO meet the corresponding sidelines of ABC in three points forming a triangle perspective to ABC.
The locus of the perspector is a remarkable isotomic pK with pivot X(264) called Euler perspector cubic.
See other locus properties in the page K646.