For changes in GOG itself, both large and obscure.

2018-04-23 - Introducing GOG Profiles

2018-04-18 - Introducing new privacy settings

2018-04-05 - GOG Support pages changes appearance

2018-03-28 - GOG Galaxy adds "friend suggestions"

2018-03-28 - Login option using Facebook credentials

2018-02-26 - GOG starts offering daily deals

2017-10-24 - Full Polish language support on GOG

2017-10-17 - Users can subscribe to release notifications

2017-09-05 - New notification system and drop-down box to access friends being (recently) online

2017-09-04 - New layout of the chat system

2017-07-07 - Chat is now for 'friends-only' by default

2017-07-06 - GOG introduces Classic Installers to keep Galaxy optional

2017-06-27 - New feature table on store pages

2017-06-12 - GOG goes China

2017-05-12 - GOG introduces offline installers with Galaxy included

2017-04-26 - Introducing the new navigation system on GOG.com

2017-04-25 - Galaxy 1.2 finally released

2017-04-21 - The game features "CLOUD SAVES" and "OVERLAY" are new filter options in GOG's catalogue

2017-04-11 - Introduction of a new font to the forum

2017-03-29 - GOG starts using proper capitalization instead of upper-case across the website (e.g. in chat and game titles)

2017-03-22 - GOG Galaxy release 1.2 marks the end of beta (Cloud Saving included)

2017-03-10 - New forum rules

2017-02-24 - Users' forum "title" extended from 16 to 50 characters

2017-02-01 - Makeover of GOG's support center

2017-01-02 - Weekly Staff Picks and Weekend Promos are replaced by Weekly Sale

2017-01-01 - First German only promo cooperation with Computerspielemuseum Berlin (Computer Games Museum Berlin) (German announcement)

2016-10-24 - Two-step login becomes default and is enabled for all accounts not having used prior opt-out

2016-08-30 - Legal agreements are changing: Virtual items loom on the horizon

2016-08-30 - Introduction of GOG Wallet

2016-08-24 - GOG.com goes Brazil, including local pricing, currency and Brazilian-Portuguese customer support

2016-08-12 - Community Wishlist maintenance: The bundling of wishes

Please feel free to post other items of interest that you feel belong here, and I will try to keep the list relevant.

2016-06-01 - Introducing GOG Connect

2016-05-05 - Six New Local Currencies Now Available

2016-03-29 - 2K arrives on GOG

2016-03-17 - Store Your Card For Later Use

2016-03-07 - Two-Step Login & HTTPS Everywhere

2016-02-05 - Developer account type added (link is to first noted instance)

2016-01-28 - Games In Development come to GOG

2015-11-20 - Stardock now boarding GOG.com

2015-08-26 - Bethesda arrives on GOG with Fallout and new additions

2015-08-24 - Gifting restrictions imposed on many games (repealed)

2015-08-20 - GOG acquires and publishes the Forgotten Realms games

2015-06-03 - First Beta Access Game On GOG

2015-05-11 - <span class="bold">My Account</span> Overhaul

2015-05-08 - Nordic Returns To GOG

2015-05-05 - Galaxy Beta Released

2015-05-05 - First Releases Published By GOG

2015-04-02 - GOG.com now also in Russian, Game Catalogue goes fully Regionally Priced

2015-02-26 - GOG.com now also in German

2015-02-25 - First Regional Locked game on GOG

2015-02-17 - New Publisher: Paradox Interactive

2015-02-12 - New Publisher: Warner Bros. Interactive Entertainment

2014-11-11 - GOG announces Pillars of Eternity, first game here from Paradox Interactive

2014-11-07 - GOG.com now also in French

2014-10-28 - New Publisher: Disney Interactive / Lucasfilm

2014-10-14 - GOG reaches 100 Linux titles

2014-10-01 - Local Prices Update

2014-09-15 - GOG Update Status Report

2014-09-09 - GOG signs Cinemaware, first Amiga games to be sold here

2014-09-03 - GOG launches official Twitch.tv channel

2014-08-27 - Some Existing Games Now Regionally Priced

2014-08-27 - 35 Games Removed From Catalogue

2014-08-27 - GOG Now Sells Movies

2014-08-27 - GOG's New Look

2014-08-06 - Mantis Ticketing System for Galaxy (Mantis link)

2014-08-04 - Introducing: TotalBiscuit GOG Showcase

2014-08-01 - GOG sponsors Axiom eSports team

2014-07-25 - New OS search terms supported

2014-07-25 - Fixed the list view search on My Account

2014-07-24 - GOG.com Now Supports Linux

2014-07-15 - GOG releases Gray Matter, first game here from Viva Media

2014-07-14 - GOG has terminated partnership agreement with Curse.com

2014-07-02 - GOG institutes new login mechanism

2014-06-04 - Bohemia Interactive titles removed from GOG

2014-04-13 - GOG releases Risen, first game here from Deep Silver

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I'm continuing The GOG Change Tracker originally created by IAmSinistar. Thanks for all your work on this, IAmSinistar!

Added:

2016-08-30 - Introduction of GOG Wallet

2016-08-24 - GOG.com goes Brazil, including local pricing, currency and Brazilian-Portuguese customer support

2016-08-12 - Community Wishlist maintenance: The bundling of wishes

Thanks for doing this thread.

Thanks for taking the helm on this one, great work already!

Yupp, great work. I wonder what our Sinistar thinks up, now that he delegated most of his "job" :D

My projects are many, out in the world. :)

Added:

2016-08-30 - Legal agreements are changing: Virtual items loom on the horizon

What is a "virtual item" and how does it differ from a digital one?

A virtual item may only be used inside a particular digital item?

So stuff like this, only sold directly within the game instead of as standalone DLC?

I look forward to the eventual introduction of intangible items, and ultimately, imaginary items. All of which of course will still cost real money.

Probably.

Don't forget in-game money or ammo or what not sold for real money too. May also be a thing (here, I mean, because elsewhere it already is).

But... but... is it still true if they're purchased with wallet funds?