The International Phonetic Alphabet (IPA) possesses a variety of obsolete and nonstandard symbols.
In addition, the rare voiceless implosive series ƥ ƭ 𝼉 ƈ ƙ ʠ has been dropped.
Those studying modern Chinese phonology have used ⟨ɿ⟩ to represent the sound of -i in Pinyin hanzi which has been variously described as [ɨ], [ɹ̩], [z̩] or [ɯ].
This list does not include commonplace extensions of the IPA, such as doubling a symbol for a greater degree of a feature ([aːː] extra-long [a], [ˈˈa] extra stress, [kʰʰ] strongly aspirated [k], and [a˞˞] extra-rhotic [a][1]), nor superscripting for a lesser degree of a feature ([ᵑɡ] slightly prenasalized [ɡ], [ᵗs] slightly affricated [s], and [ᵊ] epenthetic schwa).
The asterisk, as in [k*] for the fortis stop of Korean, is the convention the IPA uses when it has no symbol for a phone or feature.