Although common and preferred are the main types of stock, it's also possible for companies to customize different classes of stock in any way they want. The most common reason for a custom stock is when company wanting the voting power to remain with certain type of investor. This is done by assigning different voting rights to different classes of shares.

For instance, one class of market shares would be held by a select group who are given ten votes per share while a second class (common stock) would be issued to the majority of investors who are given one vote per share.