The following are free online math manipulatives that you can use with your students. I have seen them be used when doing a PD session by Dr. Theresa Wills. During her classes, she provides the links to the sites that best match the problem she is presenting, encouraging students to go and use them to communicate their thinking. She usually presents 4 tools and encourages students to show their thinking using more than one. Students can screen capture or copy what they have created into a group slide/document, showing their thinking and helping them communicate with their peers.
Math Manipulatives:
Unifix Blocks: A simple drag and drop tool that allows students to create stretches of blocks. They can represent anything from patterns to measurement to ratios. 
Cuisenaire Rods: Quickly drag the control to create bars of different sizes. Click and drag them onto the mat. They can be used to represent anything you need.
Ten Frame: The Ten Frame was a new manipulative for me as a MS/HS teachers, but I feel it is important to be aware of all the tools students may have used in the past that they connect with. I can see how this can also be used to help with integers. All students need to do is drag and drop.
Number Line: I use a number line in my class all the time when exploring ratios, rates, integers or just general problem-solving. The tool requires just a few students to start playing with it to see what it can create. Also, the information button provides a clear explanation of all the tools. Have students create their number lines, take a screenshot, and share them with the class.
Algebra Tiles, Base 10 Blocks, Number Lines and More: This site provides lots of visuals tools. By having the blocks and number lines in one location, students can easily combine the tools together to represent what they are wanting to create. There are also backgrounds that can be used that can support algebraic reasoning.
GeoBoard: Just like in person, but now without the hassle of trying to find elastic bands or having the plastic nobs break off. Students can use this to explore various geometric representations.
Fraction Bars: Create your own fractions in either a rectangle or a circle. You decide how many parts it is out of and then add the colours as you need. This is a great tool for students to quickly create the fraction bars they are wanting to represent, make them the same size and compare values.
Pattern Blocks: Never lose the blocks again. Students can pull as many as they need to their board, manipulate the direction and copy/paste to create patterns. There is a protractor that snaps into place to measure any angles. This can use used for patterns, geometry and number sense. There are also backgrounds that have shadows of shapes, allowing students to cover them with the tiles.
Additional Resources:
- Math Learning Centre: Many of the tools listed above are on the site. There are others as well as additional resources to explore
- DiDax Virtual Manipulatives: Some cross over with those in the Math Learning Centre, but there are a few new ones: 120 board, balance boards, spinners and more.
- Math Playground: Many of these require Flash to work which may cause problems with access by students. However, there are lots of options here as well.
- Geogebra Graphing and Calculator: This site provides a geoboard, calculator and graphing software. Students can save their work for later review.
- Desmos Graphing: Students can quickly create a graph, build a table of values or write a function. When finished, they can screenshot the image and add it to their work.
- Desmos Scientific Calculator: Use this as the class scientific calculator, making it easy for everyone to have access and talk about how to use the same device.
