Though the words sound identical and are spelled almost identically as well, still there is a vast difference between them.

 All Ready: It means to say that something is absolutely completed or prepared. It’s used to emphasise the preparedness of something as opposed to using just ‘ready’. For example:

 They were all ready for the meeting.

 She was all ready and looking forward to the evening.

  

 Already: It is used to show something that has happened before time or has happened unexpectedly earlier than planned. It is mainly used as an expression of surprise in sentences. For example:

 They are here already?

 She had already sent the applications by the time he called.