Phonetic keyboard v.0.6 (link) is designed to enter phonetic symbols. It was implemented with a focus on transcribing West African languages but can be used quite flexibly. In addition to basic Latin symbols, Phonetic Keyboard Layout v.0.6 contains a wide range of special symbols including consonants, vowels, diacritics, as well as some mathematical symbols. The keyboard is Unicode compatible and can be installed under Windows.
The special symbols of the layout along with key combinations that produce them are given below.