yeah, agreed, indeed (used to show agreement, confirmation or resignation)

(Brazil, idiomatic, colloquial) can you believe it? (rhetorical question asked in disbelief or dismay)

(childish) introduces a riddle

nobody's perfect (a person’s imperfections should naturally be accepted or forgiven)

time is money

no smoking

a promise is a debt; used to demand or encourage someone to live up to his promises

knowledge is power

to err is human (everybody makes mistakes)

(idiomatic) been there, done that (assertion that the speaker has personal knowledge of a particular topic)