Appmantle Sans is a modified version of Rubik's 5 weight Roman fonts. The only difference between Appmantle Sans and Rubik is that the the double-storey a has been replaced with a single-storey ษ, as can be seen in the Appmantle logo.
For more information about these fonts, see https://github.com/googlefonts/rubik
Licensed under the SIL Open Font License (v1.1)