Within Visual Basic, I had created a game similar to that of Agar.io which would match the user up with cubes instead cirlces, and the cubes have AI rather than being other users. The game which took about a day to create allowed the user to control a dynamic object that would eat objects smaller than it and have to avoid the objects bigger than it. Along with this a controls menu was ceated to allow the user to buy powerups etc...
Once the 'Play Now' button was clicked, the user would be taken to the randomly generated field and would have to try to avoid the bigger obstacles and eat the smaller ones. Along with this the AI was dynamic meaning that they would also be trying to avoid/eat each other. 
While playing the game there is an ability for the user to buy powerups by pressing 'E' this allowed the user to open the menu and therefor buy upgrades that could make the game harder and/or easier for the user.