Rainbones
Donald E. Knuth and George Miller along with Stan Isaacs made a plastic toy, rainbones, using interlocking arcs. The pcs have to lie flat on the plane, i.e. Rainbones can only realize (2D) planar solutions.

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The 'Warmup' is a partial solution, involving the 1, 2, 4, and 5 bones. These can also be done with LangTominoes.