A good local web filter. Most, if not all computer geeks (and a lot of others for that matter) know about the HOSTS file, it is easily edited and deleted, so really, for someone over the age of 5, this is not a good choice. There are a couple web filters out that are hard to install, configure, and maintain while having to go rooting through config files to even get it working. This isn't just for schools, per se, obviously it could be used for in home also. I would like it to be written in C# or VB.
A good grade and attendance suite. Again, there are some grading and attendance programs out there that are not very easy to install. A lot are web based, which I don't think is the way to go (though it does have advantages over locally installed programs). But there are also a lot of problems that I, personally, don't think the advantages make up for. Maybe C++ and Qt if I am feeling adventurous.
Other programs are for businesses. There are _many_ mediocre to good programs out there for businesses (small, medium, or large). Most are open-source and have lost any sparkle they might have had before. The others just don't have any distinguishing features that make them stand out against big-name competitors, such as bad interfaces, customer tracking, etc...
Finish the POS system. I have been working this for a while, but always end up scratching it and starting over. I can't decide if I want to write it in Qt, Gtk#, or WinForms. I think VB is the obvious choice for a language since it is excellent in dealing with XML and such. The database is also one thing that makes me second-guess my self over it. Should I use MySQL? MSSQL? Oracle? There are so many choices that it makes it difficult sometime. I have already gotten the integration with GnuCash down (much like QuickBooks POS and Quicken), it is just XML. I would offer it free to small business ( > 10 employees) with minimal networking. The rest would need to buy registration keys.
There are others, but I have still got them rolling around in my head. They are little half-baked ideas that I would write, put out the source code, and fix bugs when they came. No active development really. If you have anything that you think Linux is really missing, drop me a line.