Anyway to fully install apps and programs safely?

[RavenSword]

So, I'm noticing that some programs I uninstalled left behind some files and bits and I'm wondering if there are any recommended programs or ways to clean up these without damaging the computer or anything like that? I'm worried about poking too deep into the computer for fear of deleting something I shouldn't. Any ideas?

 

[anon(9602380)]

So, I'm noticing that some programs I uninstalled left behind some files and bits and I'm wondering if there are any recommended programs or ways to clean up these without damaging the computer or anything like that? I'm worried about poking too deep into the computer for fear of deleting something I shouldn't. Any ideas?

UPDATE for OS X 10.9 Mavericks and later: It has been discovered that on these versions of OS X, Finder may not produce search results from Library folders unless the search is started in the Library folder, even if System Files are included in the search criteria. You can either perform the following search once for your entire computer, then repeat it from the Library folders, or you may elect to use a Finder alternative app such as ​

[*]Click the + button below the search term to add criteria, then click the search criteria drop-down and select "Other...", then "System files"
[*]Click the "aren't included" and change to "are included"
[*]Sort by name, kind, date, etc. to identify components of the app, such as folders, .plist files, cache files. etc.
[*]Delete all files and folders related to the app.
[*]Don't empty your Trash until you've determined that everything is working OK, in case you need to restore something you deleted by accident.
[*]A reboot might be necessary to completely remove some apps.
[/LIST]
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Edit: In some rare instances, an app may create hidden files or folders. In such instances, follow steps 6 and 7, then repeat those steps to add another criteria, this time choosing "File visibility" > "Visible or Invisible". Then proceed with the remainder of the steps.

 

[RavenSword]

Is it even possible to accidentally delete files that are critical to the OS? Or would I get a warning or something?

 

[RavenSword]

Anyway, I reinstalled OS X El Capitan from the App Store just to be safe.