Gummy rollers
This system relies on a sticky substance like tar or glue that could be used to slow a descent. I'm imagining something like paint rollers on the hands and feet, which would either be coated in a sticky substance, or slowly exude it from a reserve tank. As the user descends, the rollers peeling away from the wall will sap some of the downward kinetic energy. The rollers could be motorized to control the rate of descent, or even driven backwards to allow a user to slide up a building.
Something like flypaper might work, but a static sticky surface will become less effective over time as it accumulates dust or other contaminants. That's why I suggest a slowly oozing, thick liquid, which would constantly be refreshed and not lose sticking power over time. You might need to do some handwaving to get a futuristic nanofluid with sufficient sticking power, however.
As an added bonus, your characters will make cool slug trails as they descend buildings! Similar to how combat divers are informally referred to as Frogmen, this special unit might be referred to as Slugmen.