Since the days still only contain 24hours (sometimes they even steal a second) I don't have the time to put most of my weird ideas into reality. So here are some of my ideas for you to pick and to become rich and famous or one of the thousands of sole open source developers that know both users of their software by first name ;-)

• a plugin for your preferred IDE to create database migration scripts based on code changes on JPA annotated classes. So if you rename a field in a classs it would rename the matching column. If you add a field, it would add a column and so on. In the second version it should support refactorings on these scripts, like merging a drop column and a create column to a rename column script and vice versa.
• an iphone app that allows to make measures with the iphone. If you accelerate the iphone from a starting point and stop at some other time one should be able to calculate the distance travelled from acceleration and duration. I'd be curious what the size of the error would be from that kind of measurement.
• an iphone app that works like an sonar. You would produce a ping with a speaker and analyze what you receive through the microphone. From that you might be able to estimate the size of the room you are in. Of course you may as well look up from your iphone.
• another iphone app: take a photo of your poker hand, and a photo of the board and get the odds for your hand calculated.
• visualize a class diagram in a 3D graph and use a wii remote and the technique shown at TED to convey the 3D impression.
• a PL/SQL language plugin for eclipse (or any other decent IDE), with the usual support for refactoring and the like.

What are your ideas for software projects that you just haven't enough time for?