FlicFlac is a tiny open source tool for converting music files between various formats.
To use the program you must first choose your preferred output format (WAV, MP3, FLAC, OGG and APE are supported). Select MP3 and you're able to choose a few encoding parameters, too.
Next, you can manually choose your source files (or just drag and drop them onto the program).
And finally you get to watch as FlicFlac uses various free tools to convert your files into their preferred format (flac.exe, lame.exe and so on), saving the finished results into the same folder as the source.
The program does have a few other small useful extras. Optional Explorer integration makes it easy to carry out your preferred conversion from the right-click menu, for instance. While an INI file helps you to customise all kinds of low-level settings and options.
Although, if you really want to make the tool your own, you can download the (AutoHotkey) source code and amend it to do whatever you like.
If you're simply looking for a quick and easy WAV/ MP3/ FLAC/ OGG/ APE conversion program, though, the core tool will probably be good enough, and as it's portable (no installation required) it's very easy to find out: just download FlicFlac and see what the tool can do for you.