The point is with an app you can have a REAL crawler and not just a tactical skirmish system. With an app you can have both tactical combat and a real dungeon to discover, plus horny surprises (traps, mysteries to solve, machine puzzles, music, real decisions).
And i imagine that with some thinking you can even have a Versus mode powered with an app (random battlefield and so on).
For the rest you already have Middara, GloomHaven and others.