ashlar-vellum cobalt. its nowhere near free unless you know where to look.
i was spoiled with ashlar-vellum long ago and have since been unable to put-up with anything else since. its incredibly intuitive and works exactly the way i want it to. i have tried several others since, including the latest offerings from autocad and solidworks and always get frustrated quickly and go back to ashlar.
i should note i only use CAD as hobby and NOT work so i use it intermittently and dont have the time or patience to properly learn all the ins and outs of any program. thats the great thing about ashlar, i dont have to waste time learning it, as most everything just works exactly the way i would think it would work.