(N) sets the NULL_GLOB option for that pattern:

    % print doesnt-exist*
    zsh: no matches found: doesnt-exist*
    % print doesnt-exist*(N)
    (doesn't print anything, pattern is just ignored)

([n]) is array indexing to get entry n; -1 gets the last entry:

    % print a*
    a-1 a-2 a-3
    % print a*([-1])
    a-3
    % print a*([1])
    a-1

Globbing is automatically sorted by name.

So putting that together, things like this:

      ~/.local/share/gem/ruby/*/bin(N[-1])  # Ruby

will use the latest Ruby version in ~/.local/share/gem/ruby, and it won't error out if it doesn't exist (so I can freely copy this around even to machines without Ruby, or remove Ruby, etc).