This client writing on python with GTK2 Frontend.

11.11.2008: Thanks to Kosmos for a new feature in 0.0.9.2.4. Open magnet-link from browser.

How you can get this:

Opera: Tools->Settings->Additional->Programs->Add protocol magnet, program is simpledcpp

Firefox: Open firefox, type about:config in address bar, create string property "network.protocol-handler.app.magnet simpledcpp". Open Settings->Applications->magnet->Use other (Set here real path to simpledcpp program).