Are made, according Wiki: http://de.wikipedia.org/wiki/MIAG

(see "Nutzfahrzeugherstellung")

I must admit, that until 5 min ago I didn't know that company either - as several of other tractor-brands in this museum, too.

AFAIK there were more vehicle-manufacturers in your town, not just MAN-Büssing.

If you want know more, I recommend this magazine:
http://thumbs3.ebaystatic.com/d/l225/m/mfYgRqSAh5Za9lk_NiiNqqg.jpg
Although it's nearly 30 years old, it's very detailed - and cheaper than books with the same content.
You can buy it for 1€ on flea-markets, that's enough. If you want, tell me your address, that I can send you a double issue.
Of course nowadays you can find much more information in the Internet, but it's a good starter and also a good summary-register.