Other ideas and links

local announcements websites

For buying/selling secondhand, etc. Better than ebay because you meet the person face-to-face and put money in the hand. No third parties pinching fees, no stupid rules, no sending stuff from the other side of the planet. This requires some trust, which builds community.

• craigslist.org international
• freecycle international, free stuff only.
• le bon coin france
• gumtree UK
• quoka.de deutschland
• loquo.com barcelona
• tutti.ch CH

swap books and other things

• swaptrees.com comparison of book swapping websites in different countries
• readitswapit.co.uk uk book swapping site

other

 open source ecology
 RAM pump using water flow to pump a small amount of water