I have issues when attempting to use a current OSX on my Mac eco system, causation - specific needs on three or four key apps. My systems comprise of MacMini, MB Air, MB Pro on OSX 10.8.5 Mountain Lion, with an additional MacMini using El Capitan (for trial purposes) plus an iPadAir2 and an iPhone - both on iOS 9. I joined the Mac eco system (from Windows) at Snow Leopard and happily used this for all of my needs; moving through Lion (quickly) and onto Mountain Lion, where I remain a happy user ! Failure to progress onward in OSX terms stems from..... my extensive libraries of photos were worked up on iPhoto ‘09 (8.1.2) - which met my needs exactly - I have numerous albums in which the photos need to be sorted Manually - ie, not by Date, Oldest/Newest or Title order ! So, the current Photos app doesn’t work as well for me on album photo sorting, albeit it apparently permits single photo movement by mouse ? I make ‘heavy’ use of iCal using many individual Alert entries (of my choosing as to day, time etc) and not the very limited Alert options afforded by the (iOS-like) latest versions of iCal, where I resort to Custom-making Alerts each and every time ! I avoid changing or making Alerts in iOS 9. I am an avid spreadsheet user and delayed moving onto Numbers from Excel. I moved platforms during Mountain Lion and live happily on Numbers now, with copies stored online as well. On attempting to work in El Capitan, I am "obliged" to upgrade my spreadsheets to the latest Numbers app and cannot then use the upgraded version on my Mountain Lion systems (where I still have unadulterated copies !) - similar events occur when using Pages; the lack of backwards connectivity is a major drawback as I seemingly need to retain Mountain Lion OSX to use my other “core” apps to meet my needs ! Are there any “clever” apps or workarounds to overcome any (or all) of these “drawbacks”, to enable update onto El Capitan OSX (and forward to Sierra in due course) ? Do I need to start using a different Calendar system to have usable Alert options (which strays away from the eco system) ? Should I revert to using Windows Excel (and/or Online) for my spreadsheets to have cross-OSX usability ? Thanks.