I would love to see a player start a MUTUAL or HEDGE FUND. This is actually noted in the User Guide (copy below).
You would make your money by charging a fund administration fee to the other players that give you their money to manage. (This fee is sometimes called a “Load Fee” when managing mutual funds).
You could use a shared Google spreadsheet to keep track of your fund investments and share that with other players.
Fireyscorp is right about how the underwriter fee works. An underwriter fee is not the same as a brokerage fee. Underwriter fee collected by an Investment Bank only applies to share issues on the PRIMARY market. Shares traded on the SECONDARY market have a brokerage fee charged by GoVenture World (not other players.).
As the game gets bigger and more players are in, there will be more opportunity for an Investment Bank to make money. And we will build more ways to spend money at some point too.
From User Guide: https://goventureworld.com/user-guide.html#investment-bank
Manage Mutual Funds and Hedge Funds
An Investment Bank, through its Holding Company, can purchase stocks and bonds just like any other business. It can also raise money from other players. This allows an Investment Bank to create its own mutual funds or act as a hedge fund and invest on behalf of other players, by conducting due diligence, negotiating investments, and tracking and reporting performance. These tasks are done manually by the player that owns the Investment Bank. See Investment Portfolio for more details.