▁of ▁. NET ▁Framework ▁by ▁X im ian , ▁introduced ▁in ▁ 2 0 0 4 . ▁It ▁is ▁free ▁and ▁open - source . ▁It ▁is ▁now ▁developed ▁by ▁X amarin , ▁a ▁subs idi ary ▁of ▁Microsoft . ▁ ▁Universal ▁Windows ▁Platform ▁( U WP ): ▁An ▁implementation ▁of ▁. NET ▁used ▁for ▁building ▁U WP ▁apps . ▁It ' s ▁designed ▁to ▁un ify ▁development ▁for ▁different ▁target ed ▁types ▁of ▁devices , ▁including ▁PC s , ▁table ts , ▁ph able ts , ▁ph ones , ▁and ▁the ▁X box . ▁ ▁Each ▁implementation ▁of ▁. NET ▁includes ▁the ▁following ▁components : ▁▁ ▁One ▁or ▁more ▁runtime ▁environments , ▁e . g . ▁CL R ▁for ▁. NET ▁Framework ▁and ▁Core CL R ▁for ▁. NET ▁Core ▁ ▁A ▁class ▁library ▁▁ ▁The ▁. NET ▁Standard ▁is ▁a ▁set ▁of ▁common ▁APIs ▁that ▁are ▁implemented ▁in ▁the ▁Base ▁Class ▁Library ▁of ▁any ▁. NET ▁implementation . ▁The ▁class ▁library ▁of ▁each ▁implementation ▁must ▁implements ▁the ▁. NET ▁Standard , ▁but ▁may ▁also ▁implement ▁additional ▁APIs . ▁Trad itionally , ▁. NET ▁apps ▁target ed ▁a ▁certain ▁version ▁of ▁a ▁. NET ▁implementation , ▁e . g . ▁. NET ▁Framework ▁ 4 . 6 . ▁Starting ▁with ▁the ▁. NET ▁Standard , ▁an ▁app ▁can ▁target ▁a ▁version ▁of ▁the ▁. NET ▁Standard ▁and ▁then ▁it ▁could ▁be ▁used ▁( without ▁re comp iling ) ▁by ▁any ▁implementation ▁that ▁supports ▁that ▁level ▁of ▁the ▁standard . ▁This ▁enables ▁port