Make a number puzzles with solutions from Brain Food. Many such problems are available, see for example As Easy As 1234 from MathsChallenge.net

Make 24, can you make 24 from the numbers and operations given? 

4 Numbers Math Game – regular puzzles published, see also 4nums.com

Countdown: Excellent programs for both games can be downloaded free from Chris Farmer’s CSF software site.
For a challenge – try the Nrich resource Countdown Fractions.

Puzzles from ilovemathsgames.com, content designed by Emily Hughes

Connect Three (NRICH)

Got It (NRICH game)
The first player who hits the given target wins the game.
Experiment with different targets and sets of numbers.
Can you answer the questions on strategy?

Remainders (NRICH)
Explore division and remainders, then try to guess the number chosen by the computer in as few attempts as possible.

Dominoes Magic Rectangle (NRICH) – form a magic rectangle then a square with Dominoes.
You can use the NRICH dominoes environment. For the traditional set of dominoes, choose a set size of 6.

Fractions and Percentages Card Game (NRICH game)
Match cards with the same value – memory game.

This game from mathFROG allows you to practice the correct order of operations against the clock.