Does Apple provide a web site with content of `man` pages for the command-line commands bundled with Mac OS X?
The old online index seems have to vanished. You can however find the source code of manual pages on https://opensource.apple.com/. This site hosts historical versions as well.

For example:


fputs(3) - https://opensource.apple.com/source/Libc/Libc-1272.200.26/stdio/FreeBSD/fputs.3.auto.html
ls(1) - https://opensource.apple.com/source/file_cmds/file_cmds-272.220.1/ls/ls.1.auto.html
grep(1) - https://opensource.apple.com/source/grep/grep-28/grep/doc/grep.1.auto.html


Unfortunately there is no overview of all manual pages, so you have to manually check directory indexes or use something like site:opensource.apple.com/source "ls.1" in DuckDuckGo or Google.