In the other thread being referred to (in the first reply) I pointed to
openSIS (for the benefit of people who find this through a search). It is much more limited in scope and intent than Moodle, which has similar aims to Blackboard (an overpriced and underperforming blot on the good name of software sold by a company with aggressive and effective patent lawyers). (I should make it very clear that my disparagement is aimed at Blackboard, not Moodle.)
CMS/LMS systems like Moodle are end-to-end systems, well-suited to online and part-time education, where student resources and submissions online are important. SIS systems like openSIS are meant to be an adjunct to traditional full-time classroom education, giving students, parents and administrators access to grades and evaluations. When choosing between the two types of systems, it helps to know what you need. A CMS/LMS may be overkill for some uses, leading to unneeded overhead in configuration and maintenance; a SIS may be missing features you need.