http://store.steampowered.com/sub/252184/
click on one of both games, and "install" the package now to get the collection, (you can close the installation window without installing the game and still get to keep it)

http://store.steampowered.com/app/265590/The_Red_Solstice/
Free for 48 hours
(Link in comments, bc the preview breaks it again...)

Click on the gamebanner and on the game's page you can click install to get it for free (you don't have to install it, you can after that simply cancel the installation)
http://store.steampowered.com/app/209670/Cortex_Command/

Click on the gamebanner and on the game's page you can click install to get it for free (you don't have to install it, you can after that simply cancel the installation)
http://store.steampowered.com/app/209670/Cortex_Command/

https://www.humblebundle.com/store/amnesia-collection