The aim is to achieve a nationally agreed consensus on how cases are collected, organised and used for teaching and examination and thereby achieve a collective common ground/platform/standard for radiology education across the country. The OsiriX UK user group are a group of Radiologists in the UK who are keen on digital radiology education and use OsiriX/Horos for teaching.
It is for these reasons that we do not list OsiriX Lite in our recommendations. Pixemo also produce a free demo version called 'OsiriX Lite', however there are major limitations placed on this including pop-ups asking you to upgrade to the paid version, performance restrictions, image viewing restrictions and inability to edit the meta-data attached to DICOM images - for example you can't easily re-order series within a study, which may be important if you are preparing cases for teaching or examinations.
There is a paid version of Horos called 'OsiriX MD', which is produced by Pixmeo, however it is expensive so not ideal for basic teaching purposes, although has great functionality.