In a Unixy filesystem, where is the conventional place to put software you're working on? [closed]
It depends on your usage plans. If this is code you want to hack on, typically your home directory is the right place, since this is private to your unix user. I personally make a 'dev' subdirectory and put code in there (mine or other people's, via github).
If you're looking to install this software system-wide, the answer varies slightly by the system. /opt is a reasonable choice in most cases, as is /usr/local.