TraceWrangler is a trace file toolkit running on Windows (and on Linux, using Wine) that supports the new PCAPng file format which is now the standard file format used by Wireshark. The most prominent use case for TraceWrangler is the easy sanitization/anonymization of packet trace files (sometimes called "capture files" or "packet captures"), removing or replacing sensitive data while being easy to use.
File and tasks
TraceWrangler generally works on a list of files. It doesn't matter if there's only one file in the list or hundreds. A couple of things can be performed using the pop up menu of the file list, but most things require creating a task and configuring its actions.
The reason for being Windows only is that TraceWrangler is written in Delphi VCL, and the compiler can only produce Windows binaries at this time. The reason for choosing Delphi over some cross platform language is pretty simple: I could have spent years on learning a language well enough to be able to code a tool like TraceWrangler - or use those same years and start the project right away, with a language I already know. Well, know enough.
Also, you can always run TraceWrangler in a Windows VM if you have to. I agree that it's not as good as a native version, but right now there's not much I can do. I also heard that it runs without problems on Wine, but I haven't checked myself.