Old, obsolete & abandoned MPEG layer 1/2/3 encoders:

LAME Ain't an MP3 Encoder

8hz-MP3 MP3 encoder
Audioactive Production Studio and Player
Blade MP3 encoder
CannaMP3 MP3 encoder
Coding Technologies MP3pro encoder
DropMP3 encoder for Mac
Electronic Cosmo MP3 encoder
FhG l3enc MP3 encoder
FhG MP3enc MP3 encoder
FhG Fastencc MP3 encoder
FhG/Opticom MP3 Producer
FhG ACM and QT codecs
FhG MP3 Surround
FhG mp3HD lossless encoder
Gogo-No-Coda MP3 encoder
M3E MP3 encoder
CDex mp2enc MP2 encoder
MP3 Compressor
MpegDJ encoder
MPecker/MPegger/N2MP3 encoders
Philips Multichannel MP2 encoder
Plugger MP3 encoder
PlusV M3V encoder
QDesign MPEG audio codecs
Iomega RecordIt
rJPa MP1/2/3 encoder
SCMPX MP1/2/3 encoder and player
Shine MP3 encoder
SoloH mpegEnc
Sound Limit MP1/2/3 encoder
Ultimate [MP1/2/3] Encoder
Ulead MPEG Converter
Uzura MP1/3 encoder
Wav2mp MP1/2 encoder
X-codec MP3 encoder
Xing/Helix MP3 encoder
YunaSoft MP3 encoder

Weird & rare & old lossy formats:

ALF2 CD codec
Astrid/Quartex AAC
AudioLib (PAC)
AudioVeda (ePAC)
AUPECg2
LBpack
QDesign Music Codec
Mafuka encoder and decoder
Entis Lab MIO
MPEGplus SV4/5/7 - Musepack
NTT TwinVQ encoder
Yamaha SoundVQ
Sony SonicStage (ATRAC)
SoftEncode AC3 encoder
K+K Research TAC
Arminio Grgic's WavSquiq

Ancient lossless audio compressors:

Advanced Digital Audio
Marian's a-Pac
AudioZip
Dakx Wav
LiteWave
LosslessAudio
LTAC/LPAC
Pegasus SPS
RKau
Sonarc
Shorten/mkwACT
Split2000
VocPack
Wavarc
WavPack
WaveZip/MUSICompress
Emagic Zap

Old voice codecs:

NTT DualSpeech vocodec
Echo Speech vocodec
QualComm PureVoice
Voyce Tech SpchComp
DSP Group TrueSpeech
Voxware vocodec

Old MPEG2/MPEG4 AAC encoders and decoders:

BITaac AAC player
Compaact AAC/MP4 encoder
Emuzed MP4 encoder
Homeboy AAC encoder, decoder and Winamp plugin
Liquid Audio
MBsoft AAC encoder and Winamp plugin
PsyTEL AACenc and Fastenc
Nero AAC encoder and decoder

Old/rare players:

AT&T a2b music
AMP MP3 player
Apollo player
Dice VQF Player
DigiDeck MP3 player
FhG IIS MacPlay3
FhG IIS WinPlay3
Foobar2000
iMPload complete MP3pro
K-Jöfol player
Métis MP3 player
MicroHof MP3 Player
MP3 Jukebox for Win3.1
MP3 to EXE
MP3 to EXE (another one)
Musearc player
NAD player
Nullsoft DOSamp MP3 player
Philips MPEG Audio player
RealJukebox
Sonique2 alpha MP3 player
SoundApp Mac OS Player
WinMusic for Win3.1
WWV VQF player
XAudio player
XingSound MP2/XingMP3 player
Yamp player

Misc. rarities:

nyaochi's ACMENC
ACM Station
AudioCatalyst CD ripper
CoolEdit audio editor
CoolEdit/Audition import/export filters
EAQUAL - Evaluation of Audio Quality
Exact Audio Copy CD ripper
EncSpot MP3 analyzer
MixMP3 line-in recorder
MPEG Audio Creator CD ripper
Tag and Wapet taggers