Freewaregenius has reviewed Office Tabs [website].
Made by another company, free for personal use.

Hi, yes, simple and intuitive.. neat.

I found v6 and v7 (v7 is quite new) work with Word, Excel, Powerpoint 2003. v6.51 crashed Word 2003 (only) on launching Word.

(Vista, 32 bit). On v6.51, the developer said he'd look into it.. and now we have v7.

http://www.extendoffice.com/product/office-tab.html
shows the differences between the free and paid versions.

Although this said the free version allows customisation (the default tabs position really should be on the left of wide screen laptops, not the top), I found it didn't.. 

Odd thing with v7:
In Powerpoint 2003, Vista 32 bit, just using 'New' document (blank) the first tab is Doment1, but hit New again and Document2 tab overlays it. Hmmm.

Next is Document3, but closing those and- hey, there's no Document1.

This doesn't happen in Word or Excel.

Also if you manually close e.g. Document 3,2,1, so you have no documents open, then open another one, it's Document4.. I'd have expected (maybe it's just me) Document1. Being more extreme, if you had 13 tabs, closed them all and opened another, it becomes Document14..

-this is normal behaviour for the way Office works.

also in other programmes - Untitled 1 etc,
I presume they work up from "1" in one sitting/session and only go back down to 1 again when restarted