A self-sealing tire isn't a run-flat tire in the sense that it can operate without air. Instead, it has a layer of sealant inside the tire that can maintain the air pressure in the event of a puncture. If you get a nail in the tire and remove it, the sealant will fill the puncture as long as it is near the center of the tread and is not larger than 5 millimeters.
The biggest advantage of the self-sealing tire is that it resembles a traditional tire. It can be mixed and matched with standard tires, and the tread life is the same. The downsides are the higher cost (roughly the same premium as a run flat tire) and restricted availability.
This type of tire isn't standard on new vehicles but is worth mentioning since it is available as a replacement tire. Continental and Pirelli are two tiremakers that produce self-sealing tires.
Make an Informed Purchase
Run-flat tires seem to have more downsides than upsides, but many people swear by them. Take the time to read customer reviews and know what tires come standard on a car before you buy.