Refers to all people in a group; often used in formal or written contexts. Slightly more emphatic than みんな.
Refers to all things; less common than the 'everyone' sense. Often used in set phrases or literary contexts.
Everything doesn't always go as one wishes.
I wish good health to all of you.
Everyone in the hall applauded.
Alternate spelling without iteration mark; less common but still used.
Reduplication of 皆 (みな, 'all, everyone') for emphasis. The exact historical derivation is uncertain, but the form is attested in classical Japanese.