GOG Installers are based on the InnoSetup and are offered in 2 versions currently
Galaxy Cloud is a feature of the GOG Galaxy client that allows save game data to synced to the Cloud. This feature is made available to the public in version 1.2. List of games that support cloud synching can be filtered on the store or very first list of Galaxy Cloud games can be seen on this page.
Although Universal Cloud Saves in Galaxy Client needs to be implemented by the developer, some games Planescape: Torment, Heroes of Might & Magic III, or Vampire: the Masquerade - Bloodlines received the first time save syncing in the cloud .
While the Galaxy client for Linux is still in development, an unofficial client for GOG has been created using Python, while using LGOGDownloader to download any game through the old API used by the GOG Downloader. The client features the built-in launcher for each game, integration with Wine, DOSBox and SCUMMVM and configure it for the specific game, applying community patches and more. It is currently in a Prototype state, but usable and installation is very simple by just running the install.sh script, make sure to download the required dependencies to get it to work properly (Besides Wine).
A simple GOG client for Linux that lets you download and play your GOG Linux games.
GameHub allows to view, download, install, run and uninstall games from supported sources. GOG is one from official sources among Steam, Humble Bundle and Humble Trove.
Lutris is a gaming client for Linux. It gives access to video games and has integration with GOG store which allows to import existing game library and community maintained install scripts which provides a completely automated setup.
C:\Program Files (x86)\GOG Galaxy\GalaxyClient.exe
Sales on GOG.com happen in regular basis, the most recent one called Weekly Sale, which starts in each Monday at 11 AM GMT, additional games are added to it in each Friday at the same hour the sale starts. Big sales usually happen a week or two before Steam's happens and adds themed bundles on sale, along with single games in every day. The best moment to redeem Steam games to GOG.com via GOG Connect is when the sale is coming to an end.