一个比较强大的提供各种形状的ImageView

github上比较老的项目了，但是还是比较好用的。
各种形状总有一个满足你。
在自己的项目中使用，最好不要将所有的类都导入进来，取自己需要的就可以了。

<com.github.siyamed.shapeimageview.BubbleImageView
        android:id="@+id/image"
        android:layout_width="50dp"
        android:layout_height="42dp"
        app:siTriangleHeight="8dp"
        tools:src="@drawable/neo"
        android:layout_alignParentLeft="true"
        app:siArrowPosition="right"/>

<com.github.siyamed.shapeimageview.CircularImageView
                android:id="@+id/relative_test_img_1"
                android:layout_width="60dp"
                android:layout_height="60dp"
                android:layout_margin="8dp"
                android:layout_weight="1"
                android:src="@drawable/placeholder"
                app:siBorderWidth="6dp"
                app:siBorderColor="@color/darkgray"
                android:layout_alignParentLeft="true"
                android:layout_centerVertical="true"/>
<com.github.siyamed.shapeimageview.RoundedImageView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="8dp"
                android:src="@drawable/neo"
                app:siRadius="6dp"
                app:siBorderWidth="6dp"
                app:siBorderColor="@color/darkgray"
                app:siSquare="true"/>

<com.github.siyamed.shapeimageview.mask.PorterShapeImageView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="8dp"
                app:siShape="@drawable/triangle"
                android:src="@drawable/neo"
                app:siSquare="true"/>

            <com.github.siyamed.shapeimageview.mask.PorterShapeImageView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="8dp"
                app:siShape="@drawable/octogon"
                android:src="@drawable/neo"
                app:siSquare="true"/>

            <com.github.siyamed.shapeimageview.mask.PorterShapeImageView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="8dp"
                app:siShape="@drawable/star"
                android:src="@drawable/neo"
                app:siSquare="true"/>
<com.github.siyamed.shapeimageview.DiamondImageView
                android:layout_width="250dp"
                android:layout_height="250dp"
                android:layout_margin="8dp"
                android:src="@drawable/neo"
                app:siBorderWidth="8dp"
                app:siBorderColor="@color/darkgray"
                android:layout_gravity="center_horizontal"/>

            <com.github.siyamed.shapeimageview.PentagonImageView
                android:layout_width="250dp"
                android:layout_height="250dp"
                android:layout_margin="8dp"
                android:src="@drawable/neo"
                app:siBorderWidth="8dp"
                app:siBorderColor="@color/darkgray"
                android:layout_gravity="center_horizontal"/>

            <com.github.siyamed.shapeimageview.HexagonImageView
                android:layout_width="250dp"
                android:layout_height="250dp"
                android:layout_margin="8dp"
                android:src="@drawable/neo"
                app:siBorderWidth="8dp"
                app:siBorderColor="@color/darkgray"
                android:layout_gravity="center_horizontal"/>

            <com.github.siyamed.shapeimageview.OctogonImageView
                android:layout_width="250dp"
                android:layout_height="250dp"
                android:layout_margin="8dp"
                android:src="@drawable/neo"
                app:siBorderWidth="8dp"
                app:siBorderColor="@color/darkgray"
                android:layout_gravity="center_horizontal"/>

            <com.github.siyamed.shapeimageview.HeartImageView
                android:layout_width="250dp"
                android:layout_height="250dp"
                android:layout_margin="8dp"
                android:src="@drawable/neo"
                app:siBorderWidth="8dp"
                app:siBorderColor="@color/darkgray"
                android:layout_gravity="center_horizontal"/>

            <com.github.siyamed.shapeimageview.StarImageView
                android:layout_width="250dp"
                android:layout_height="250dp"
                android:layout_margin="8dp"
                android:src="@drawable/neo"
                app:siBorderWidth="8dp"
                app:siBorderColor="@color/darkgray"
                app:siStrokeCap="round"
                app:siStrokeJoin="round"
                android:layout_gravity="center_horizontal"/>

            <com.github.siyamed.shapeimageview.StarImageView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_margin="8dp"
                android:src="@drawable/neo"
                app:siBorderWidth="8dp"
                app:siBorderColor="@color/darkgray"
                app:siStrokeCap="round"
                app:siStrokeJoin="round"
                android:layout_gravity="center_horizontal"/>

Android开源：SImageView - 方便实用的图片控件
http://www.open-open.com/lib/view/open1482459625909.html

Library for display a few images in one MultiImageView like avatar of group chat
https://github.com/stfalcon-studio/MultiImageView
Android-Snowfall
https://github.com/JetradarMobile/android-snowfall