I singlespeeded my Dahon Mu XL frame and modified it with some light parts:

* Wheels: Kinetix Pro
* Tires: Kojak
* Tube: Schwalbe XX Light
* Cranks: SRAM RED carbon
* Innenlager: GXP
* Pedals: Wellgo MG1 TI
* Seatpost: SDG I-Beam
* Seat: SDG FX
* Chainring: TA Alize, 49t
* Chain: KMC X10-SL
* Sprocket: Reverse single speed kit, 13T (Transmission: 49T front to 13T rear)
* Brakes: Avid Single Digit SL/Speed Dial SL, 482g (w/o cables)
* Cables: Shimano XTR
* Bar: RaceFace Carbon, 98g
* End Caps: 6g
* Grips: KCNC

Didn't weight it yet, should be around 8kg.

more details and pics including some parts-on-scale pics in this forum (German)