Today, Opera Software has introduced a major change to the redistribution model of the Opera browser. Like Google Chrome and Mozilla Firefox, the stable release channel of Opera will get a web-based installer in the near future. Opera Dev branch has already got it so anyone who is interested in staying on the bleeding edge of browser development will be able to play with the installer stub.
However, if you need to install Opera on multiple PCs, you would want the offline installer of Opera. Instead of downloading the setup on every PC, you can download it once and then install it everywhere.
The offline installer is also helpful if you use some expensive or limited mobile Internet data plan.
Thankfully, the offline installer is available for stable releases.
I suggest you to bookmark this page to get updated instructions for the stable release instantly.