seriously, if there is any good idea for a piece of software (sounds like you mean a small one) then it's been done. It may be hard to find, but it has been done. If there is any software idea that hasn't been done yet, it's because no one thinks it is a "good" idea. If you can really think ahead of your time maybe you can think of something, but that's exceedingly hard to do. My advice: if you have free time to burn programming, contribute to some open source project, preferrably one where you will learn a lot.
BTW, 99.9% of software in industry is just writing code to keep up to standards, IE, getting a C compiler to work on hardware platform X. Most of it is reinventing the wheel, sadly.