Here are two I like in particular. They change BitD in a way that works well with their unique settings.
Crimson Blossoms:
Only three attributes, no action ratings. Uses narrative traits, like Fate Aspects, which can “blossom” and “wither” to add +1d.
Band of Blades:
Having different rewards/penalties depending on the type of mission (assault vs recon, etc).
CrashCart: How the deck of cards is used and also the patient sheets. The patient sheets especially are great at concisely delivering both world building and complications.
Antiquarian Adventures: All the special abilities, especially how characters have to flee, bungle something, etc. to get composure back.
Flesh and Metal: Harm affecting different parts of the body.
Moth-Light: Doubt and how it can build up after each session and create conflicts that feel natural.
Those are great. I was looking at CrashCart. Looks really unique.
I really like the Resist mechanic from Wicked ones.
You roll an Action which cannot have weak effect.
Failure: You spend 3 stress to partially resist the consequence.
Mixed: You spend 2 stress to partially resist the consequence.
Success: You spend 1 stress to fully resist the consequence.
Critical: You clear 1 stress and fully resist the consequence.
I really dig the Heart & Glory Resist mechanic, where you can pay the stress cost of another die in your Resist roll to resist consequences an extra time, and how armor gives you an extra die on that roll.