Twitter is experimenting with a new feature, called fleets. With fleets, users will be able to tweet which will automatically disappear after 24 hours.
Currently, this feature is only offered to Brazilian users, but Twitter says that this feature will be released gradually to other countries as well. If the flats were released to all users, they would change the way people interact with each other on Twitter.
In practice, the flats will be more like an Instagram story than an ordinary tweet. In other words, Twi