There are thousands of quality typefaces you can embed in your app at affordable prices. Both myfonts.com and fontspring.com, two of the most popular commercial font sites, offer licences for app embedding.
As others have mentioned, there are lots of high quality open source fonts too. For example, Adobe's Source San Pro, designed by Paul D. Hunt, is popular on many websites. It was designed for UIs and comes in a whole range of weights:
As others have mentioned, there are lots of high quality open source fonts too. For example, Adobe's Source San Pro, designed by Paul D. Hunt, is popular on many websites. It was designed for UIs and comes in a whole range of weights:
https://github.com/adobe-fonts/source-sans-pro
Another font designed for UI display is Clear Sans commissioned by Intel:
https://01.org/clear-sans
When looking for a font, the quality can vary widely, but the choice is enormous.