You don’t really need a plugin for that. You said you read the forum post about “launcher” so you have missed this post? It only uses pure JNI functions from C#. No additional plugins are needed.
I haven’t tested it myself. He doesn’t dispose any of the java objects he creates which is actually quite bad. It should be something like this:
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Of course to use this you need to pass the “bundle identifier” / “package name” of the other app. For example subway surfers has: “com.kiloo.subwaysurf”.
I’m not sure if “OpenURL” works with market links to send you to the appstore. You have to try it for yourself.