you might look into Psychopy and its online platform Pavlovia. There you find many tests for memory, and you could download the experiment for free and run it on Psychopy.
Well, you haven't mentioned that you need to test online. So yes, if you need that, Pavlovia is not for free. However, if you are affiliated to a university they can buy the licence. If not, jsPsych might be an alternative.
Sequencing Test WOM-ASM: You will see a series of balls on the screen. The user will have to memorize the series of numbers and repeat the sequence. The sequence will first be made of just one number, and will increase by one number each time until the user makes a mistake. The user will have to repeat the sequence after each presentation.
Concentration Test VISMEN-PLAN: A series of three objects will appear on the screen, and the user must remember the order in which they appeared. The objects will disappear, and the user will have to remember the series in order to choose the correct option on the screen.