Homepage:

• News section

Game detail page:

• Review section
  
• Activity input box

• Get the latest version here:
  https://github.com/DukeDukeEm/DukesCleanSteamUI/releases
  
  
• Unpack the zip to: c:\Program Files (x86)\Steam\skins\
  
  
  
• Select the skin in Steam's settings under the 'Interface' section.
  
  
  
• Restart Steam

In short:
I wanted my library to organize and start games. Nothing more.

The long version:
I use my library mostly as a game laucher, and it bugs me to always see new content where I just want to organize and start my games. The news section covers ~1/3 of my available space and is non-removeable. It doesn't belong to the library-part of the interface.

I'm only one click away from any game-specific (game details page) or account-specific (activity page) news. Then there's the News Hub, which can even be my main startpage. Additionally I can opt to read the news in a notification-popup on startup. Really important news I get through the 2 notification icons in the top-right corner of the client.
Plenty of opportunity to read the news.

Steams UI could easily allow me to add/remove this section.
But it doesn't.
I think having the news there is a good default setting for all the people which don't care or just want to have everything on the startpage. But forcing it on everybody isn't very nice.

That's a way of shoving content down my throat I didn't ask for.
What I also didn't ask for is getting asked questions all the time.
Do I like this game? Should I think about it later? Should I write a review?
I do not think it is a bad thing to remind people to rethink and shout out their opinion, but I think it's bad to be forced into it as someone would be some sort of underdeveloped human being.

I like to keep all that news/shopping/social stuff in my browser where I have more control over it. A good example for that would be Augmented Steam[augmentedsteam.com]. It adds price comparisons, store/search/market-customizations & is open-source. But it only works with Firefox, Chrome or Edge, not with Steams internal browser.

The following screenshot shows how I use my own startpage.
Some categories at the top and a recent-games list below, nice and clean.
I additionally enabled 'Low Performance Mode' in Settings>Library to remove sluggish hover-effects and random coloring on the category-buttons.

I personally decided to change the way Steams UI works in the most unintrusive way possible.
Which means there are no more tools needed than Steams own ways to change the UI (through the now mostly unused skin feature).

But if you want more, there's another way to change the Steam UI.
Jonius7 created an external patcher to change the client in a more in-depth way.
Check it out here: https://github.com/Jonius7/SteamUI-OldGlory

Pro: much more features
Con: higher risk to break something when Valve decides to implement new stuff in the future