For the most part there are no special features.
There are however differences in the gauge wire used, number of wraps, spacing between wraps, amount of wicking used, amount of airflow provided, and amount of juice flow provided.
There are two notable exceptions though. The Freemax Starre and Uwell Crown both have dual parallel wrapped coils. That means that rather than a single wire there are two wires running side by side in the coil.