AMD Athlon 64 1500+
Released in november 2005 as low-power (9W TDP) Athlon 64 CPU. It doesn't have the IHS (Integrated Heat Spreader) to make the physical dimensions smaller and lighter and to help increase heat dissipation.
As far as I know this CPU was not sold in boxed versions through regular OEM-channels. The CPU ended up in blade systems like HP BladeSystem bc1500.
Theoretically it can be run in regular S754 motherboards but I haven't tested that yet.