Last Java Collection Library Files

Last Java Collection Library is accessible via Central Maven Repository.

So if you build your project with Maven 
then you shouldn't download its jar file manually. 
Just add following maven dependency:

<dependency>
   <groupId>net.sf.lastjcl</groupId>
   <artifactId>lastjcl</artifactId>
   <version>1.1</version>
</dependency>

If you use good old Ant then use contents of this folder.
But former method is much more convenient and modern.
See http://maven.apache.org