OP's answer overlooks the top one way to fund a new business: your first customer.

Think about it, most of us already have everything we need to go into a software business: a computer, bandwidth, a little gray matter, a little desire, and a decent chair. All that's really missing is a customer.

Find someone who is willing to pay for something, build it for them, and get paid. You've just knocked off multiple birds with one stone.

Funny how often this is overlooked.