I bought "good old games" on different online stores. Maybe you know, what is online one day it could by offline next day. I decided to download all the games with additional content from such websites. There are many tools which could automate everything for you but I was more interrested into simple command-line script.
What I'm missing from such tools is to keep track of downloaded files (index) because I would like to move the content to different drive.

GOG

There are several scripts or full apps which download content from GOG. Usually they fully support to download all content, extras included. I tried first minigalaxy which unfortunatelly showed just a few games from my collection. Next one was gogrepo.py script which looked promissing but unfortunatelly there was again problem. I got all extra content but was not able download game itself.
And then came wyvern. I compiled it from source (Rust) into single binary and run it. Had some problems with login because of GOG captcha, so generating OAuth token was the solution. Wyvern is simple for use, I just didn't find way how to download all extra content for all games in one shot. I had to go game by game ID and run the command. This could solve simple shell script but for a few games I'm lazy to write it:-)

Humble Bundle

I found very useful script for downloading all the content humblebundle-downloader. Very simple tool but first step is a bit uncommon, you have log into Humble Bundle website, getting session cookie and passing it to the script. It was a bit tricky because of special characters in the cookie itsel. (Trick)[https://github.com/xtream1101/humblebundle-downloader/issues/40] is mentioned in the issue tracker to add backslash with quotes at the begginning and end of the cookie - for example \""cookie content"\".