Speex
Xiph.Org's free speech codec from 2002, built for VoIP and later retired in favour of Opus.
Where Vorbis was made for music, Speex was made for voices. Jean-Marc Valin based it on CELP, the same idea behind mobile phone codecs: rather than describe the waveform, the encoder models the vocal tract as a filter and sends only its parameters. Speex handled narrowband, wideband and "ultra-wideband" (8, 16 and 32 kHz) and coped reasonably well with packet loss.
It turned up in early VoIP clients, game voice chat and Flash Player. Valin then went on to co-create Opus, which covers speech and music alike, and Xiph declared Speex obsolete. Rare is the codec whose own authors tell you to stop using it.