A number of newer ones are ventless (although still very much the minority in North America), but only some use an actual heat pump to recycle the heat. IME most of the cheaper ventless dryers just reject the heat (but not the moisture) into the room they're operating in.

This is still a win because it doesn't depressurize the house (any air you vent out of the house is eventually replaced by outside air, sometimes via dirty areas like crawlspaces and attics). But the heat pump ones can run off of a low-power (~1500W) circuit whereas the condensing ones typically need a higher power (~5kW) circuit.