The attached files contain a template for manually creating a small network barter deal during a presentation, barcamp session or other social gathering. The template is for up to 5 people with up to 4 offers each, but you can extend it. It has not yet been tried in a live environment, so better do that before real-world use 
Instructions for use:
- Delete prices and orders. This should be done before the session starts. It will render all cells in dark gray for being "inactive".
- Collect participants. Replace dummy user names (user 1, user 2 etc.) with real user names. In both line 1 and column A.
- Collect offers and prices. Replace dummy item names (product 1-1, product 1-2 etc.) with names of real products and services people want to offer. Be sure to mention the unit and max. available quantity in the cell for the name, or in a comment on it. Services can be offered by the hour. Prices for each product go into column C and should use the official currency of the location for simplicity. When entering a price, the line will become light gray, showing that the product is available for incoming orders.
- Collect orders. Users may order anything offered by the other users. Orders are placed by entering a number of how much to order (1, 2, 1.3 etc.) into the light gray cell belonging to a users column, and to a product's line.
- Balance. This is the hardest part, usually done by the Makerfox, but now you have to
(on a small order graph only, though). Look at line 25 (user balance). Users with a positive balance have to order more, users with a negative balance have to sell more. Let affected participants make proposals for new orders and / or cancelling orders to get balances closer to zero. Needs some experimenting and time. Some users might even wish to drop off completely to make the deal work. - Execute. Once all users are at balance zero in line 25, everyone sells as much as they get. That's a valid network barter deal, and you can tell everyone to deliver the goods and services they sold according to the barter matrix.
Note: If the field “balance of balances” (I25) is non-zero, there is a bug in the form. It should never happen.
Licence of attached files: Creative Commons Attribution 4.0 International. Files uploaded by request of @Nadia.
file_fid:14065 - barter matrix template (LibreOffice / OpenOffice – original file, for best results)