A colloquial negative copula meaning 'is not' (shortened form of ではない).
これはリンゴじゃないよ、梨だよ。
This isn't an apple, it's a pear.
今日は休みじゃないから、会社に行く。
Today isn't a holiday, so I'm going to the office.
君のせいじゃないから、気にしないで。
It's not your fault, so don't worry about it.
A colloquial sentence-ending tag used to seek agreement or confirmation — 'isn't it?' (shortened from ではない).
いい天気じゃない？散歩に行こうよ。
Nice weather, isn't it? Let's go for a walk.
その色、似合うじゃない。
That color suits you, doesn't it?
もう遅いから帰ろうじゃない？
It's late already, so shall we go home?