Geoboard is a wonderful web-based app (at https://apps.mathlearningcenter.org/geoboard/) that can also be downloaded for free from the App Store and Google Play. It is suitable for all students especially those working on learning about geometric properties in the elementary grades.
Different sizes and shapes of boards can be chosen by clicking on the appropriate choice on the bottom toolbar.
If needed, grid lines and numbers can be added:
The wonderful thing about Geoboard is that you have an infinite supply of unbreakable elastics that cannot be lost or flicked across the classroom. Students will quickly learn how to drag an elastic from the ones shown onto the board and then how to grab and drag a side to create different shapes. This allows the teacher then to set challenges that will get the students to think more carefully about geometric properties such as ‘Make as many isosceles obtuse triangles as you can’:
Other options on the tool bar that can be used include the ‘Fill All Bands’ as well as a drawing tool.
Another useful tool is the ‘Duplicate Item’ tool:
Clicking on this will create a duplicate shape which reveals options to rotate or to reflect horizontally or vertically:
More ideas about the types of questions that can be asked using the Geoboard app can be found in this blog post: http://themathguy.blogspot.com/2014/02/geoboards-in-car.html