There are no prisons. Crimes are punished with fines or with exile. Criminals are exiled from nations, not from the world government. An exiled criminal must leave the nation and go to another nation. The exiled criminal cannot go a nation which refuses to accept the exiled criminal. For example, suppose one nation makes islam illegal. If someone is convicted of practicing islam and is exiled, then the criminal will probably have no problem being accepted in some other nation which does not prohibit islam. But someone who commits robbery or murder will probably not be accepted in almost all other nations. However, there are a few nations which accept anyone. These nations are like prisons. These prison nations are mostly nonvoting. The national governments of these prison nations are mostly dictatorships. These prison nations are very poor because the labor force is not very productive, and because taxes are high because the cost of keeping order is high. The criminals who are sent to the prison nations have no sentences. Any criminal may leave at any time if the receiving nation is willing to receive the criminal.
If you are a murderer, and you are sent to a prison nation, you can probably get a job working for the dictator, because the dictator will always need to have some troublemaker beat up or killed. But if you accept such a job, other nations will be less likely to accept you, so it will be harder for you to get out of the prison nation.
Nations are partly responsible for the behaviour of their citizens. If the citizen of one nation travels to another nation and commits a crime, then the other nation may demand compensation from the home nation. If a nation cannot guarantee that a citizen will not commit crimes in other nations, the home nation should exile the citizen.
The economies of the prison nations are based on unskilled labor intensive industries like making clothes, sorting garbage, and growing vegetables and flowers. There are few capable administrators in the prison nations, so many of the prison nation industries and government departments are run by telecommuters who live outside the prison nations.
The prison nations are more like third world nations than like conventional prisons.
Some public service organizations run criminal rehabilition programs in the prison nations. If the public service organization declares that a criminal is rehabilitated, and if the public service organization has a good reputation, then the former criminal will probably be accepted by the other nations and will be able to leave the prison nation.
Each public service criminal rehabilitation organization specializes in a specific type of criminal. Some help criminals who lack job skills and turned to crime because of poor job prospects. Some help criminals who were drug addicts and turned to crime to support drug use or because drug use interfered with honest employment. Some help criminals who have become disabled and are now physically incapable of committing crimes. Some help criminals who were wrongly convicted and are not criminals at all.
There are no appeals of criminal convictions. Criminals who have been wrongly convicted can usually be accepted by a nation, and so do not have to remain in the prison nation, and so no appeals are needed.
There is no discrimination against former criminals. If a national government thinks that a criminal is not rehabilitated, then that national government will not accept that former criminal. Nations will either accept former criminals or not accept former criminals. Nations will not accept former criminals but prohibit former criminals from working in certain occupations or living in certain places or possessing certain objects.