Here is a clean and minimal UI kit made with Sketch app. Freebie created and released by Mateusz Dembek.
An Android L’s tablet UI template for Sketch App. Mobile template is available too. Freebie created and released by Vincent Tantardini.
Android L tablet UI template – Sketch
An Android L’s mobile UI template for Sketch App. Freebie created and released by Vincent Tantardini.
Android L UI template – Sketch
Yosemite UI Kit for Sketch 3. All UI elements (well, besides the OS X 10.10 Icons) have been redrawn and restyled as accurately as possible.