Recently, I released my own utility on CodePlex, it is known as Sharepoint List Security Manager.
It addresses the inherent permission issue of Sharepoint Document Library, where two contributors are able to edit/delete each others document.
I personally faced this issue, while I was developing a Knowledge Base Portal, we were dealing with a lot of document libraries in this project, but unlike Lists, there was no OOTB way to set who should Read or Edit documents within the library.
Sharepoint Lists have this built-in mechanism in place OOTB, so when you go to List Settings -> Advanced Settings you can set this permission, but the same is missing for a Document Library.
I made a generic tool to set these permissions for any list/library on your server farm.
The utility allows you to set
List/Library Read permissions to: a) Everyone b) Only Author
Write permissions to: a) Everyone b) Only Author c) None
The utility is developed using Windows Forms in C#, it is very intuitive and user-friendly. You can download this from CodePlex, available here: http://www.codeplex.com/ListSecurityManager/Release/ProjectReleases.aspx?ReleaseId=23086