I thought it was ipad only?
Check the docs.marketo.com for the direct URL.
It is (or has been) available on Android as well as iOS, but Jay Jiang is correct, in that it seems to be missing from the Google Play store. In fact, the search result for the app leads to a "not found" - https://play.google.com/store/apps/details?id=com.marketo.eventcheckin&hl=en_US. Unfortunately, there's no direct link in the Marketo documentation either - just a suggestion to search the app store for "Marketo" - which only currently results in the (lacking) Marketo Moments app.