OneTrash is a tiny but incredibly useful system utility. It solves a problem pertaining the emptying of the system trash.
I have been a Mac user for quite some time now, and I love how the Trash works. However, it presents some problems from time to time. The main purpose of this app is to solve one of those problems. Basically, on Mac, you can't delete a single file or a few files from your Trash without emptying the whole thing. When you launch OneTrash, you will see an "Open File" dialog. This dialog shows all the files on your Trash. You can simply select one or more files to permanently erase them from the Trash. If you click on "Cancel", you will see a list view of the files on your trash. Apparently, this is the way the app was in the previous versions. After you have selected and deleted the files that you wanted, OneTrash will automatically quit.
On the Mac App Store, there are reviews of users who said that this app helped them to delete files that just refused to be deleted from the Trash. This is yet another problem that I experience a lot. For some reason, some files just won't be deleted.
In short, if you need to delete only a few files from your Trash, or have problems getting rid of a file, OneTrash can probably be of use.