A grid editor that leaves the craft to you
Start with your theme entries, then place black squares round them and your symmetry follows. Pick any square to see the entries that fit across and down, ranked by how well they cross, with dead ends struck out. When a corner won't fall, look through fills that keep your theme entries, and take one or keep going.
⌘-click or press period for a black square.
Pick a square to see the words that fit through it.