Motivations, popularity & ratings of each way

- popularity of each category - what are the advantages what the disadvantages - what we can learn by each way of dessiminating info and how we can combine them (for example: in a repo we can find the source of a project, in a course webpage we can find the information we need to learn how a source code works and then we can contribute or make patches etc using for example tools like bazaar,cvs,git by ourselves)