For the Linux GOG Downloader there is now an (unofficial) Debian Wheezy and Jessie Repository.

Just add to your /etc/apt/sources.list the following Line (or create a new file in /etc/apt/sources.list.d with the following line):

deb http://mash-systeme.de/debian/ wheezy main (for the Debian 7 Wheezy packages)

OR

deb http://mash-systeme.de/debian/ jessie main (for the Debian 8 Jessie packages)

After that, just do an

apt-get update && apt-get install lgogdownloader

and the newest Version (current: 2.26) will be on your computer.

You can also download these packages as always from here:

http://mash-systeme.de/downloads-view-content