Sometimes we have occasions where we want students to collaborate or work in groups rather than be working independently. Unfortunately, most apps are designed to be played individually or if students can work together, they must use a central game site which may or may not be a place you want your students.
So occasionally, it is good to organize some of the older types of games which have students actually interacting with each other.
Although Learning With Math Games is actually geared for upper elementary and middle school, there are some lovely games that can be used to scaffold instruction for high school students. I found a lovely game which helps students practice their use of integers. It requires a specially constructed deck for each person in the pair. Students add two cards together to form a sum and the one with the largest sum gets all four cards. Another game uses a regular card deck to practice exponents.
East Carolina University created created several Math Middle School Energizers which combines physical activity with math. One activity I discovered combines line dance with integers. Just think, take a 5 min physical break with a bit of music and holding up integer cards that tell students the number of steps to move left or right.
Another site, Fun Maths have several nice games for use in the classroom. I looked at the algebra egg race which came with the playing board and directions, everything needed to have students practice substituting values into algebraic expressions. Another activity requires students to spend exactly $1,000,000. To show they've spent the money, they have to create a presentation with pictures, prices, and a sheet showing the prices of what they bought. If you wanted, you could require students to create the presentation digitally or create a hard copy.
Finally is Bright Hub education with a nice collection of games ranging from "Who wants to be a millionaire" to a proportion relay which requires students to move, to a fraction game. I find that many of my lower performing students are weak in the basics and all of these sites have activities which can be used to strengthen these skills.