Comment by gcheong

Unless you have a paying customer willing to pay you with just a promise of something to be delivered (see kickstarter et al, Steve Blanks's customer discovery, etc.), you don't. If it solves a problem you have and in a better way for you than other solutions then you personally get immediate value from it. From there, it's possible others may have the same problem and will be willing to pay for it. It's not guaranteed but the number of people getting value from the software will be at least n = 1.