Is there a Mac equivalent to Windows 7's library feature?

At the risk of stating an idea too obvious to merit an answer, I will point out that ever since OS X 10.9 Mavericks, tags are perhaps the most obvious way to take "several related files in different folders" and "combine them in the same view" as stated in the original question.

In the Finder, select any item and then use the Tags... menu item (to which you can assign a keyboard shortcut in the Keyboard system preferences pane), or the Edit Tags button in the toolbar of any Finder window, to assign a tag to that item. You can then click on the name of that tag in the recent tags list (in the sidebar of any Finder window) to see a list of all files tagged with that tag. Or you can search for that tag and save the search as a smart folder. You can tag any items that appear in Spotlight search results, including email, contacts, reminders, etc. For more information about working with tags, see my answer to this question about tags best practices.

Easiest way I can think of to do it is if you bring up the file info window by pressing ⌘ + i keys, and then add something into the Spotlight Comments field that you keep the same through the files you want. Rinse and repeat for the files. Create a new Smart Folder, for the search option go to Other... and it'll bring up the full list, which will include Spotlight Comments.

I found a hint about it, the idea is to make a saved search that scopes the first folder you want, edit the XXX.savedSearch in a text editor and add other folders to the scope, so that it looks like this

<key>FXScopeArrayOfPaths</key>
    <array>
        <string>/Volumes/DD/Documents</string>
        <string>/Users/charles2/Documents</string>
    </array>

It's not exactly like library because you get all the files, though.

For documents there is an app in the Mac App Store iDocuments Lite. It seems similar to iPhoto and/or iTunes but for documents.

• Auto Import & Management
• Organize and manage documents on your Mac using collections, folders and smart folders.
• Quick tag, Open Metadata supported.
• Search the documents by small clue like keywords, title, and author's name etc.
• Auto Run, Batch process (full version)
• Click to share (full version)

There are some other features available not listed above. The app puts everyone of your documents in an easy to access library. Haven't been able to find a single app that encompasses all file types rather a separate app for music, photo's, documents etc. The Lite version in the App Store is free, might be worth checking into. The Full version is $49.95.