| Spiritually, Callisto
can trace its roots to an open source project called Zephyr Basecamp
(ZBC), also by Callisto's author.
While ZBC was a good program, various factors prompted a full rewrite. That rewrite became the Jupiter III project, which is a full featured business management system.
After awhile, Callisto (yet a further rewrite) evolved. It is in its fifth full rewrite. As good as Jupiter III is, it is too complex for smaller businesses.
If you are looking for a small buisness management application for windows or linux, take a look at Callisto.