Although Bordeaux-Threads may be more popular today, but Portable-threads offers more portable APIs (e.g. atomic-incf) and supports older versions of implementations. GBBopen also has a " scheduled-periodic-functions" module based on portable-threads, it literally supports creating "scheduled periodic functions" which is very useful in a Lisp server environment.
Dan Corkill is the one to bother regarding bugs, comments, criticism, suggestions, enhancements, and extensions.
Chun Tian (binghe) created a separated repository on Github after realized that cl-containers doesn't use portable-threads any more (the download link below is a very old version of portable-threads). This new repository contains both "portable-threads.lisp" and "scheduled-periodic-functions.lisp" from GBBopen project. He also added support for LispWorks 7.