I downloaded the OSX .pkg installer and didn't see anything in /Applications or /opt after running it and telling it to install to my root drive. Just glancing at some docs on your site I see pipeline-init, so doing a find on / to find out where it placed the binaries see it installed to:

/usr/lib/pipelinedb/usr/lib/pipelinedb/bin/pipeline-init

Is this intentional?

EDIT:

After playing around with the .pkg file it looks like the packed Payload contains '/usr/bin/pipelinedb/usr/lib/pipelinedb' which is probably the problem. I see broken symlinks for pipeline-init etc in /usr/bin pointing to /usr/lib/pipelinedb, so I'm guessing this repetition of the path above is a mistake.

Also I see a postinstall script creating a symlink from pipeline to psql. This seems like a bad idea as psql is pretty universal already as the name for the PostgreSQL CLI binary, maybe 'pipesql' might be better?