Like a GoFundMe where you announce your intentions to build a product, the early backers would be those who bought your stock helping the price to rise.
The company would need to stock split and regularly sell more shares during it's years of growth.
That said, there is a mechanism that is more, well, "direct" than the traditional IPO process you usually read about. That mechanism is known, appropriately enough, as a "direct listing" or "direct public offering." See:
https://www.investopedia.com/investing/difference-between-ip...
https://www.nyse.com/direct-listing
etc.
Note that there are still plenty of rules and regulations involved, but it is a lighter weight process than the traditional IPO. But as the linked articles note, there are downsides to DL/DPO for the company who is selling, with one of the biggest being the fact that there's is no guarantee that any shares will sell.
What you're talking about would probably be illegal in the United States unless you restricted it in certain ways.