It's not a widget it's just using styling and css transitional effects, just take a look at the html and css using google chrome inspector. I took a brief look and the following code shows the principle of it, basically if you hover over it move the top up further so that you then show the bottom half:
.appstore-tile:hover .appstore-tile-scrollarea {
top: -200px;
}
.appstore-tile .appstore-tile-scrollarea {
-webkit-transition-property: all;
-moz-transition-property: all;
-o-transition-property: all;
transition-property: all;
-webkit-transition-duration: 0.2s;
-moz-transition-duration: 0.2s;
-o-transition-duration: 0.2s;
transition-duration: 0.2s;
-webkit-transition-timing-function: ease-in-out;
-moz-transition-timing-function: ease-in-out;
-o-transition-timing-function: ease-in-out;
transition-timing-function: ease-in-out;
position: absolute;
top: 0;
left: 0;
}
.appstore-tile {
-webkit-user-select: none;
-moz-user-select: none;
user-select: none;
position: relative;
overflow: hidden;
margin: 0 0 20px 22px;
width: 218px;
height: 198px;
border: 1px solid #dfdfdf;
background-color: #f6f6f6;
}