MP3 Diags is a tool for inspecting, tagging and fixing errors in MP3 files. It is included in many of the bigger Linux distributions, and it runs on Windows and Mac as well. A number of sites provide the Windows version for download. It is pretty well documented and it has a number of features not found elsewhere, free or paid. It is also translatable (currently there are French, Czech, and German translations.)
Unfortunately I had very little time in the last year to spend on this project, and the future doesn't look that different. So it would be great if somebody with C++ and Qt knowledge would like to implement features or just take over the project.
The things to be done are to add support for some files, fix some of the outstanding bugs, move to newer libraries, or add whatever feature the developer feels like.
If interested, please write to mp3diags at gmail