This library is deprecated and no new development is taking place. Consider using a FAB(Floating action button) instead.
E.g. the Android Design Support Library offers a FAB implementation.
Circle button widget for Android
Gradle dependency  build.gradle
repositories {
    mavenCentral()
    mavenLocal()
}
...
dependencies {
    compile 'com.github.markushi:circlebutton:1.1'
}
Example Usage:
<FrameLayout
	xmlns:android="http://schemas.android.com/apk/res/android"
	xmlns:app="http://schemas.android.com/apk/res-auto"
	android:layout_width="match_parent"
	android:layout_height="match_parent" >
	<at.markushi.ui.CircleButton
		android:layout_width="64dip"
		android:layout_height="64dip"
		android:src="@drawable/ic_action_tick"
		app:cb_color="#99CC00"
		app:cb_pressedRingWidth="8dip" />
</FrameLayout>
