For what is worth, the voiced bilabial fricative is a sound similar to English "b" and "v". Languages that use that sound normally write it with "b", "v" or "w". It's common in Spanish but also creeps up in certain words in Portuguese, Japanese and others. [1]
In IPA, the standard phonetic alphabet, that sound is notated by "β" instead. The b-with-a-stroke, as well as barred-b (ᴃ) were used by some linguists before IPA became widespread, but they still kept appearing since they were easier to type in most typewriters (B, backspace, hyphen) and apparently also because some linguists didn't like IPA.
In addition, b-with-a-stroke is part of the Jarai alphabet, a variant of the Vietnamese alphabet used to write the Jarai language. [2]
In IPA, the standard phonetic alphabet, that sound is notated by "β" instead. The b-with-a-stroke, as well as barred-b (ᴃ) were used by some linguists before IPA became widespread, but they still kept appearing since they were easier to type in most typewriters (B, backspace, hyphen) and apparently also because some linguists didn't like IPA.
In addition, b-with-a-stroke is part of the Jarai alphabet, a variant of the Vietnamese alphabet used to write the Jarai language. [2]
[1] http://en.wikipedia.org/wiki/Voiced_bilabial_fricative [2] http://en.wikipedia.org/wiki/Jarai_language