OS X 10.11 El Capitan was released on September 30, 2015, as a refinement-focused update to OS X Yosemite. While it maintained a similar visual style, it introduced critical performance enhancements and several multitasking features that defined the later OS X era. Key Features of El Capitan Mac OS X 10.11 El Capitan: First Impressions
If you simply want El Capitan running again (not an ISO file), do this: Mac Os X 10.11 El Capitan Iso Download
Apple’s official method (still works)
Verification: Genuine installers should have the SHA-1 hash: 9f2ce4b6d5aec0d07da58a6a0e7a8e8c4e86e3e8. System Requirements OS X 10
Download the InstallMacOSX.dmg file directly from Apple's servers. System Requirements Download the InstallMacOSX
installer inside to place the "Install OS X El Capitan" app into your Applications Apple Support Community Unofficial ISO & Community Mirrors