VOBMerge

VOBMerge is a simple-to-use tool that allows you to join two or more VOB files.
This software doesn't require any installation. Since it is portable, your Windows registry entries will not be changed. Furthermore, you can store the app on a removable device and deploy it on any computer.
The user interface of the program is very simplistic. All you have to do is add files to the queue by either using the file browser or the "drag and drop" method, and then initiate the merging process.
Files are joined together very quickly and VOBMerge manages to keep a good image and sound quality, as well as smooth transitions, while using a low-to-moderate amount of system resources.
However, one of the major shortcomings of the program is that you cannot arrange VOB files once you have added them to the queue (the context menu only allows you to remove one or all files).
So, you will have to plan ahead and insert VOBs in their correct position from the start. Also, there are no kind of settings that you can select or configure (e.g. preview videos, change video properties).
Additionally, VOBMerge doesn't contain a help file but there's a "ReadMe" text document in the root directory that you can check out.
All in all, VOBMerge is simple enough to be handled by both novices and advanced users. Although it needs some upgrades (especially when it comes to its functions), the program gets the job done.