Main features:
Batch Tag Editing Write ID3v1.1, ID3v2.3, ID3v2.4, MP4, WMA, APEv2 Tags and Vorbis Comments to multiple files at once.
Support for Cover Art Download and add album covers to your files and make your library even more shiny.
Import from Amazon, discogs, freedb, MusicBrainz Save typing and import tags from online databases like Amazon, discogs, freedb, MusicBrainz, and more.
Replace characters or words Replace strings in tags and filenames (with support for Regular Expressions).
Create Playlists automatically Create and manage playlists automatically while editing.
Rename files from tags Rename files based on the tag information and import tags from filenames.
Export to HTML, RTF, CSV Generate nice reports and lists of your collection based on user-defined templates.
Full Unicode Support User-interface and tagging are fully Unicode compliant.
Besides these main features Mp3tag offers a variety of other functions and features ranging ranging from batch export of embedded album covers, over support for iTunes-specific tags like media type or TV Show settings, to combining multiple actions into groups that can be applied with a single mouse click.

What's New in v2.66 Final:
[2014-12-13] NEW: added support for complex JSON object values by web sources framework functions
'json_select_object' and 'json_unselect_object'.
[2014-12-12] NEW: added support for boolean values in web sources framework function 'json_select'.
[2014-12-11] FIX: MP4 cdec field for encoder settings was not preserved when writing tags.
[2014-12-11] CHG: added support for mouse wheel scrolling in tag panel.
[2014-12-10] CHG: added context-specific detection of mouse-wheel usage to prevent accidentally
overwriting the field contents.
[2014-12-10] FIX: updated RATING MM to use latest mapping of values.
[2014-12-10] FIX: removing filter from filter history did not reset filter and file list.
[2014-12-06] FIX: field RELEASETIME was missing after resetting the tag fields list.
[2014-12-06] FIX: adding cover art did not conform to the description in the documentation (select
file dialog was showing the current working directory instead of the file's directory in case no
default directory was provided).
[2014-12-06] FIX: documentation of action 'Remove duplicate fields' did not mention that the first
value is retained.
[2014-12-06] NEW: added scripting function $strcmp to compare strings case-sensitively.
[2014-12-06] NEW: added scripting function $stricmp to compare strings case-insensitively.
[2014-12-06] FIX: documentation of scripting function $eql did not mention that strings are
compared case insensitive.
[2014-12-06] FIX: scripting function $eql was not working correctly if strings contained umlauts or
diacritic characters.