Cooperative is a good company form for self-employment when a group of professionals starts testing out different kinds of business models. You do not need to have a clear business idea; you can develop it along the way. You do not need a large startup capital to start a cooperative, and in terms of administration, it is effortless to join and leave a cooperative.
Practising entrepreneurship part-time as a member of a cooperative is a good choice when you have occasional gigs. For instance, in the cultural field, there are cooperatives in which the members’ skills complement each other: one member is a photographer, another a graphic designer, third an animator and so forth. In the rules of the cooperative, you agree on how much of your income is paid to the cooperative and how much can be paid to the members as salary, for instance.
The members should have profound trust in each other. One of the members has to be more active than the others to run the administration, or the cooperative has to hire a person to take care of statutory obligations.
Before starting a cooperative, you should contact relevant authorities to find out exactly what your position as an entrepreneur will be. In principle, all company forms allow part-time entrepreneurship, but in cooperatives, it is the simplest: if the cooperative has at least seven members (and each of them owns less than 15 per cent of the cooperative) and the members are in an employment relationship as determined in the Employment Contracts Act, the members are not officially deemed entrepreneurs. Hence, a salaried worker can belong to a cooperative and still be eligible for the unemployment benefit.
Starting a cooperative:
https://www.suomi.fi/company/starting-a-business/forms-of-enterprise/guide/cooperative
Co-operatives Act:
https://www.finlex.fi/fi/laki/kaannokset/2001/en20011488.pdf
Worker cooperative on Wikipedia:
https://en.wikipedia.org/wiki/Worker_cooperative