The uncontested skinniest house in Boston was built as part of its neighboring structure. Not out of "spite" as a popular but apocryphal story goes.
Originally, 48 and 46 Hull Street encompassed the present-day footprint of 44 Hull Street too. Eventually, those two structures were split into three - with 46 and 48 Hull being converted to brick. Only 44 Hull Street (aka the "Skinny House") remains as part of the original wooden structure.
While it has been used as a short-term rental, it is now a private residence - as it has been for most of its rich history.