The following list is a summary of the programs I recommend on various pages on my website, plus some more interesting software especially for guitar players. All of them are freeware and - as far as I know - ad-free and require no registration. There are much more programs around, this is a list to start with and covers the most popular software. All links go to the authors homepage as far as he has one. Bold links show "must haves". Suggestions welcome.
Power Tab 
Power Tab Editor is a tablature authoring tool for the Windows operating
system. It is intended to be used to create guitar sheet music, more commonly
known to musicians as guitar tablature and bass tablature. (aka guitar tab/bass
tab). The program provides the most commonly used symbols in tablature,
including chord names, chord diagrams, rhythm slashes, bends, slides,
hammer-ons/pull-offs, harmonics and palm muting. A useful piece of software for
people who want to learn how to play guitar, and for experienced guitarists who
want to transcribe their own music and/or guitar lessons. The software can be
used by both acoustic and electric guitar players alike.
TuxGuitar 


A Multitrack tablature editor and player.
Audacity 


Audacity is a free, easy-to-use yet powerful audio editor and recorder. Supports some VST-plugins.
Kristal 
An older, but powerful and free multi-track audio sequencer. Supports most VST-plugins. See
more at Home Recording.
Wavepad 


This audio editing software is a full featured professional sound editor.
It lets you make and edit music, voice and other audio
recordings. When editing audio files you can cut, copy and paste parts of
recordings and, if required, add effects like echo, amplification and noise
reduction. WavePad works as a wav editor or mp3 editor but it also supports a
number of other file formats including vox, gsm, real audio, au, aif, flac, ogg
and more. You can also slow down without changing the pitch.
Wavosaur 
Wavosaur is a free sound editor, audio editor, wav editor software for editing,
processing and recording sounds, wav and mp3 files. Wavosaur has all the
features to edit audio (cut, copy, paste, etc.) produce music loops, analyze,
record, batch convert. Wavosaur supports VST plugins, ASIO driver, multichannel
wav files, real time effect processing.
Winamp 
Nullsoft Winamp is a fast, flexible, high-fidelity music player for Windows.
Winamp supports MP3, CD, Audiosoft, Audio Explosion, MOD, WAV and other audio
formats, custom appearances called skins, plus audio visualization and audio
effect plug-ins. additional features including free-form skins, a new decoder,
built-in cross fade, and an advanced Media Library.
Recommended plugins:
Take it easy (slowdowner)
Slow me down (as the name says)
Loop Master
Windows Media Player 
Inlcuded in Windows, but not everyone knows how to slow down:
--> full mode --> view --> enhancements --> show enhancements --> click on 'Play Speed Settings'
BestPractice 
BestPractice is a musician's practice tool, to slow down or speed up music,
either from an MP3 file or directly from a CD. Link has expired, but it's still
downloadable from many software archives. Just google for it.
Hydrogen 


Hydrogen is an advanced drum machine. It's main goal is to bring
professional yet simple and intuitive pattern-based drum programming.
Hammerhead 
HammerHead is a simple TR-909-like drum computer program aiming at the
dance-scene. You can use it to create perfect Techno loops, Jungle patterns or
House beats, but it's also suitable for Hip Hop, Triphop, Rap, Industrial and
almost any other music you can think of - including Blues.
Drumstation 
DrumStation is a virtual drum computer and groove studio for your PC. It is
roughly based on the legendary Roland TR-909 drummachine. DrumStation makes it
possible to create beats in CD quality without any further knowledge and in no
time. All created grooves can of course be saved as .wav data in order to be
used in other music software.
KVR VST Plugin Database 


A huge database of free plug-ins for VST like amps and effects. Can be used
with any software supporting VST plugins.
More VST:
Tobybear Productions
SimulAnalog Guitar suite
GiveMeTac. 
Simple, but good metronome.
Audio Phonics Guitar Tuner
Very good and easy guitar tuner using line-in. Many tunings. Available in the
Archive.
Digital Guitar Tuner 
Digital Guitar Tuner is a free Windows software, which let's you accurately
tune your guitar using direct input or microphone. Version 2.3, featuring 27
tuning types, is available for downloading.
Guitar Tuner 
Another tuner supporting line-in and different tunings.
WINCHORD 
WINCHORD is a compact program intended for the serious guitar player who wants
to experiment with chords. For a given chord the program shows the position of
the tones on the guitar so that one can create his own finger placement. Chord
types can be altered easily. Also one can find the chord for a given finger
placement. Furthermore the program can generate fingering automatically.
(Original link has expired.)
YGS Guitar Chords Help System 
This is guitar chord help system. More than 600 chord tabs, 37 chord types,
1122 chord letter-and-numeric names (for example Am) in this version.
Exact Audio Copy
Exact Audio Copy is a so called audio grabber for audio CDs using standard CD
and DVD-ROM drives. It works with a technology, which reads audio CDs almost
perfectly. If there are any errors that can’t be corrected, it will tell you on
which time position the (possible) distortion occurred, so you could easily
control it with e.g. the media player
AoA Audio Extractor 
With AoA Audio Extractor, you can easily extract audio tracks from AVI, MPEG,
MPG, FLV (Flash Video), DAT, WMV, MOV, MP4, 3GP video files and save them as
MP3, WAV and AC3 formats.
MediaCoder 
MediaCoder is a free universal batch media transcoder, which nicely integrates
most popular audio/video codecs and tools into an all-in-one solution. With a
flexible and extendable architecture, new codecs and tools are added in
constantly as well as supports for new devices.