I work in a small business, and we constantly run into problems that need a small but not trivial solution for a specific purpose that we assume should be fairly common in the market. We look for solutions, and then end up having to roll our own.
Examples: - We hosted a conference last year. We needed a web site to manage the conference materials and match them with the sessions that were being put on, which would allow presenters to manage/update their materials, and would be protected via passcode for attendees only. Seems like a common problem for conferences, but we found no off the shelf solutions for this, and had to roll our own. We would have rather paid a few hundred dollars and been done with it. - We need some software to handle recurring tasks, such as building/machine maintenance. It needs to easily accommodate specifying a resource and all the maintenance that goes along with it, and the intervals associated with them. The tasks should then be distributable amongst a pool of people, either through direct or automatic assignment. Pretty straightforward, but difficult to find something that isn't a big pile.
Maybe what is really needed is a web site that serves as a launching point for small business IT shops, where common problems are listed, and software is reviewed that serves to solve each problem. What happens though is that (1) it becomes ad dominated, so you can't trust the websites, and (2) it gets flooded with a million crappy solutions.
Maybe we're just especially bad at locating solutions, but I think if you really want ideas, just target small businesses that are growing, and ask their IT departments what projects they have had to develop that weren't really the company's core business. All those items would probably be target applications.
Caveats: - Price it reasonably. - Make purchase an option, rather than requiring month to month terms. Not all small businesses want to pay in perpetuity, nor can we afford to get stuck when a startup goes out of business and our service fails. Selling us the software lets us know it is going to keep working.
Anyway, more than my 2c.