The lowercase form was introduced by Isaac Pitman in his 1847 Phonotypic Alphabet to represent the voiceless postalveolar fricative (English sh).
It is not common around African languages, but it is, in fact, used in some, for example, Serer uses its lowercase form to make the [ʄ] consonant.
The International Phonetic Alphabet (IPA) uses U+0283 ʃ LATIN SMALL LETTER ESH to represent a voiceless palato-alveolar sibilant.
Related obsolete IPA characters include U+01AA ƪ LATIN LETTER REVERSED ESH LOOP, U+0285 ʅ LATIN SMALL LETTER SQUAT REVERSED ESH, and U+0286 ʆ LATIN SMALL LETTER ESH WITH CURL.
U+AB4D ꭍ LATIN SMALL LETTER BASELINE ESH is used in the Teuthonista phonetic transcription system.