This is similar to Masyu, but has two key rule differences.
This puzzle appears in "Challenge Your Brain Math & Logic Puzzles" (Dave Tuller & Michael Rios, Puzzle Wright Press).
Puzzle and Goal
An unsolved puzzle consists of a rectangular grid; some cells contain white circles.
The goal is to draw a single open path that satisfies the clues.
The solved grid must satisfy the following conditions:
The path must turn 90° in each white circle.
The path must turn 90° exactly once between each pair of white circles.
The path must visit every cell.