The new operating system for recent Mac computers is now available for free from the App Store in your Mac's Applications folder.
It's called El Capitan, OSX 10.11 and first reports are favourable. Some new features including more comprehensive Notes should keep everyone happy. Mail has been completely re-written, a necessary fix as the last version in Yosemite, Mac OSX 10.10 caused some problems.
It's named after a huge rock in the Yosemite National park so rock-solid performance is what we're expecting.
If your trusty Mac is older than 3 years or so, or doesn't have more than 4GB of RAM I wouldn't advise it....El Capitan is a modern operating system assuming a contemporary machine. Best with minimums of 8GB RAM and an i3 processor, unless you like moving at a slow pace.
Here's a comprehensive page with pretty much all you need to know about it: