The SAGE/SageMath CAS is free software, maintained by volunteer enthusiasts. This has pros and cons, of which I have experienced a handsome dose in the last couple of days. Starting with the cons: every hotshot programmer-mathematician who feels a ferocious urge to maintain an up-to-date step-by-step installation guide for dummies, please raise your hand now ... Uh-huh, thought so. Besides, none of those guys could do that job anyway, even if they wanted to: by the time anyone starts to take such things seriously, familiarity has already blinded them to many of the difficulties faced by a newcomer. Thus the download file directory comprises large number of alternative file identifiers, with no clue how to distinguish (say) sage-8.9-OSX_10.14.6-x86_64.app.dmg [for my operating system] sage-9.1-OSX_10.11.6-x86_64.app.dmg [for latest CAS release]. On randomly downloading some not-obviously unsuitable selection, one might (eventually) succeed in finding a way past Apple's security to click hopefully on the nice blue icon, calling up a browser panel labelled "Jupyter" which looks very business-like, but cannot apparently be persuaded to actually DO anything. At which point your newbie rolls up a sleeve and falls straight into a novice trap: he opens the installation README file, and attempts to execute the procedure described therein in deceptively precise and comforting detail. Then rolls up the other sleeve and tackles the Q&A support site, which has lots of Q's and A's and a search option, but (naturally) no procedure apparent for actually submitting an enquiry. Eventually all these obstacles prove to be minor, given a modicum of dogged perseverance, which proves rewarded by a couple of major pros. The level of support is astounding: once broken into the frankly weird bug-report system, my query was responded to within minutes by a fellow user, who pursued it through the weekend. And when one does succeed in invoking it, the software appears robust, efficient, cleanly designed, fast, (relatively) compact. For the benefit of anyone else contemplating installing SageMath on an Apple iMac, there is now a step-by-step description in the author's answer at https://ask.sagemath.org/question/53036/installation-fails-at-readme-step-5-... which tries to carry on from where https://doc.sagemath.org/html/en/installation/binary.html http://www.mirrorservice.org/sites/www.sagemath.org/osx/intel/index.html leave the novice dangling. Fred Lunnon