Patented K. Walker & designed with H. Nelson, made by Binary Arts, circa 2000.
(four plastic pieces, 4 x 4 x 3/4 inches assembled)

The four pieces do not simply come apart as it appears they might; careful positioning and twisting is required; here is the solution that was sold with the puzzle:



Further Reading

Walker Patent, from: www.uspto.gov - patent no. 5,409,227