If you have been working on projects independently and not under a professor, does compiling your work on a personal website/blog also serve as a good reference for an admission committee looking to select a graduate student for a Master of Science program? Or should a professor always vouch for the work you do? Thank you.
No, realistically a list of external projects will not make up for not having letters.
Letters are typically not, or not primarily, used as a description of projects you have done, but as a subjective evaluation of your potential as a
PhD graduate student. Letters may include a discussion of undergraduate research, but will also include a discussion of your personality, especially your strengths and weaknesses as a researcher. It is evident that this cannot be learned from a description of projects alone, especially given that this list is curated by yourself.
Incidentally, this is also the reason why senior professors are considered the "best" references - admission committees assume that the best judge of prospective grad students are those you have seen many grad students succeed and fail, i.e., senior professors.
Edit: as jvb correctly notes, the question is about master rather than PhD applications, but at least for a master by research, this does not change the spirit of my answer. For masters by coursework, I think most universities don't really employ a competitive selection procedure anyway (at least the ones I know don't).
Depends :) If your pet project is
gcc or some part of the Linux kernel (to give a computer science example), or something else which is well-known and actually in use somewhere, or a successful commercial product, it might serve this purpose well. And of course it's interesting to get to know the candidate a little bit.
On the other hand, I wouldn't be overly impressed by most un-reviewed work. (Incidentally, this includes work of professors and workgroups, too.)