It looks like everything Krin has made was in the Flash era, so whatever program he used is no longer practical. That being said there are a couple of good choices. The most common, which happens to be free, is the Unity game engine, which is fantastic if you're a programmer. If you're not a programmer you simply won't be able to make the same types of games, or use the same programs to make them. A good choice for non-programmers that I know of is the Construct engine. It's a free (paid to use a lot of the features) game engine that doesn't require any programming knowledge.
