You can do that right now in every modern socialist country, but what about the USSR and the Warsaw Pact? And any future socialist and communist experiment(s)?
By self-employment, I'm indeed referring to running your own business, but I'm referring to a sole proprietorship or freelancing, not your typical business where other workers are exploited for the benefit of the owner.
USSR had small-scale coops called 'артели', and sole proprietorships weren't even regulated IIRC. In some Warsaw Pact countries like Hungary it was even allowed to organize small-scale businesses with hired labour.