MakeItOne MP3 Album Maker is a free app that can merge multiple MP3s while maintaining full reversibility (the ability to unpack/split the file into its original constituents at any later point). Merged files can be played on any player and MakeItOne and can preserve and edit the audio file tags and add album art as well. It can also unpack audio files packed by the Albumwrap shareware app which are commonly found on the net.

Possible uses are up to your imagination, and include merging disparate chapters or parts of an audiobook into a single file, archiving and organizing albums, and creating a single file for easier publishing or sharing on the net.

MP3 Diags is a free program that can scan your audio library for problems (including issues with invalid streams, low quality issues, incomplete tags, audio normalization, and others) and provides the ability to fix these. It includes an audio tag editor that can pull track data from MusicBrainz and Discogs, and can use MP3Gain from within the MP3Diags interface to perform audio normalization. Note, however, that this program is not geared for users looking for a 1-click fix, but rather for users with some technical background. MP3 Diags is multiplatform (Windows/Linux)

MetatOgger is a free, powerful program for tagging and renaming MP3s and other audio files. It offers the functions you would expect from a tag editor (e.g. mass renaming, tags from filenames or path, scripts to perform editing functions) as well as a few that are not so common, such as “acoustic fingerprinting” of unknown songs using the MusicBrainz database, built in album art search, importing lyrics from lyricwiki.org into your audio tags, and the ability to download a massive audio tag database that it can use as a tagging resource.

ATunes is an open source program that combines a powerful, full-featured music player with a Last.fm-powered recommendation engine. Available features include CD ripping, internet radio, audio podcasts, smart playlists, support for portable audio devices, and others.

Album Art Downloader XUI is a free program that can download and save album art into your music folders. It is designed to scan your albums for missing album art and perform simultaneous multiple searches in batch. It also offers shell integration for quick album art lookups on the folder level.

BBox Audio Player (BBoxV2) is a free lightweight audio player/manager that offers a good range of features including CD ripping, audio file tagging management, internet radio, automatic volume normalization, audio library management functions, and others.

Mp3ListShellEx is Windows Explorer shell extension that allows you to create playlists or text lists of your MP3s simply by highlighting a folder and selecting an option from the right click context menu.

JRiver Media Jukebox is an advanced music manager that has recently turned 100% freeware. It provides most of the tools that you will ever need to play and manage your audio library, including audio format conversion, CD burning and ripping with online tag and album art support, full smartlists support, a tag editor, Ipod and device management, podcast support, sound recording, ad-hoc album art downloading, visualizations, skins, and extendibility through a wide range of freely downloadable plugins (including a pre-installed Last.FM audioscrobbler plugin). It supports most audio file formats.

IArtwork is an Itunes add-on that scans your Itunes library for available album art. It can then either downloads all missing album art en-masse and/or allow you to manage individual album instances individually.

MediaCoder Audio Edition is a free, full-featured audio conversion program that can both read and write to almost all popular audio file formats as well as audio streams in video files. MediaCoder AE contains all the necessary codecs it needs for encoding/decoding audio within the standalone software.

AlbumArt.org is a site that provides searchable CD and DVD art in large format.