Harmony Workbench
Most chord tools hand you symbols. This one shows you the voices — because a progression doesn't sound classical or cinematic because of which chords it uses, but because of how the inner lines move between them. Build a progression, watch the four voices, and let the suggestions tell you why a chord works. Every suggestion is ranked partly on voice leading the tool actually computes.
The smoother the lines, the more the progression sounds like writing rather than chord-changing. Held and stepping voices are what make a change feel inevitable.
Want the reasoning behind these moves — why ♭VI and ♭VII feel the way they do, what a suspension is actually delaying, and how a descending bass carries a whole song? That's in Writing Harmony, which also covers the 4AD and darkwave vocabulary this tool is stocked for.