The aim is to allow a simple technology to work in a wide variety of different screnarios.
Most web users are familiar with the Paypal 'donate' button (). An analagous 'donate via EDGE' button could have a simple mailto: link to their Email address underneath. Users with an EDGE capable Email client would simply click on this to bring up a donation pane.
Request For Help
The tip jar described above is a special case that fixes the currency (e.g. as $). To request help of any particular kind, the currency should be fixed by a corresponding URI, semantic web style. For example, to request furniture the identifier http://giftflow.org/find/gifts/?category_id=6 could be used. More general requests for help would drop the requirement that the evaluation must consist of a specific currency, and let the donor choose the type of help they wanted to offer as well as the amount.
Unsolicited Offer of Money or Other Help
To donate to someone, whether of money, goods or services, it is sufficient to send them an unsolicited evaluation by Email. If their Email client had EDGE support (unlikely for strangers), it would be handled as above, as an incoming donation. If not, it should be crafter in such as way as to display something to the effect of "this is an EDGE donation, click _here_ to learn more".
An invoice is a reverse donation, a "You Owe Me" rather than an "I Owe You", so it is an EDGE evaluation with a negative amount. e.g Donate someone -4 hours of their time to ask them for 4 hours of help from them.
Friends Of Friends
The "Coincidence of wants" issue means that there is a lot to be gained from passing on gifts from friend-to-friend. This is a more complex case to be handled later, but one that may influence the design so is suitable for the discussion page.