Wget is a free utility for non-interactive download of files from the Web.  It supports HTTP, HTTPS, and FTP protocols, as well as retrieval through HTTP proxies.

Using Wget to download entire website:

Step 1. Create directory where you are planing to store the website content:

mkdir /home/user/offline_site

Step 2. Go to directory that you just created:

cd /home/user/offline_site/

Step 3. Use following command to download the website:

wget -r -Nc -mk http://www.debian-tutorials.com/

NOTE : Command explanation:

-r Turn on recursive retrieving
-N Turn on time-stamping
-m Create a mirror
-k Convert the link

After completion all content will get downloaded into your directory.

Done.