There are several kinds.
1) Group financing based on ownership shares; with this type of financing, in return for their investments, the investors receive an ownership share which may or may not imply voting rights. It all depends on the legal structure of the investing platform, which may be in the form of a share in the company, SPV, collective, etc. This kind of group financing is called "crowd investing".
2) Group investing based on loans; this type of investing is based on micro-loans between two parties on the platform. The loans may or may not include an interest rate, and this model can sometimes overlap with the above explained group financing based on ownership shares - depending on the business model by which the group investing platform works.
3) Group investing based on rewards; investors do not receive a financial return on their investments. Instead, they acquire certain perks which the project initiator decides upon, and uses in order to attract investors. The rewards can take many forms, but are generally either goods, services or acknowledgements.
4) Group investing based on donations; the case in which a large number of people donate money with no compensation. A merit of group investing as opposed to group donating is the transparency of spending, and the ability to address specific issues or individual situations of individuals requiring help.