For instance, after WWII, America loaned Germany money so they could pay their reparations to Britain and France. Then Britain and France took that money and paid back their loans from America sending them weapons. Did this involve the actual exchange of cash or was it just more like "I'll pretend I give you this so you can pretend to give me that."
For Germany, this was mostly outlined at the Potsdam Conference (http://avalon.law.yale.edu/20th_century/decade17.asp)
It was much more complicated than a straight cash IOU. Most of the reparations came from the dismantling of the remains of Germany's war machine, and sending machinery and manufacturing plants to the UK, France, and the Soviet Union. There was a division and distribution of intellectual property. Annexed territory was ceded to other countries. And forced labor from POWs was also used for reparations.
To further complicate the post-WW2 German balance sheet, you also need to factor in the WW1 debt that was defaulted in the 1930s that Germany decided to pay back after WW2, and the Marshall Plan later disrupted the de-industrialization plans and added a new set of loans and grants to the picture. (See http://www.marshallfoundation.org/library/documents/Marshall_Plan/Reports/Foreign_Assistance_Act_of_1948.pdf)
The Paris peace treaties of 1947 (http://digicoll.library.wisc.edu/cgi-bin/FRUS/FRUS-idx?id=FRUS.FRUS1946v04) outline the reparations of the other Axis countries.