haha I forgot about Axure. They're so expensive though, but that's where I got my start as a UX person. Is their product still relevant for startups and freelancers w/ a tight budget?

it's not 'cool' enough

Came here to say exactly this - Axure is brilliant for this sort of thing.

Axure's variables are especially powerful when combined with states. For example you can create components with logged in and logged out states and use a global variable to determine which gets shown when. So you could set the logged in variable to true when clicking a login button and the page would update to show the logged in component states. Much better than creating two different pages and transitioning between the two.

You can also animate individual components, which Marvel and other page-based prototyping tools struggle with.

Also Axure's had responsive components and shared libraries for years. Even though it's 'uncool' and a bit ugly I'm impressed by its power every time I use it.

Expensive yes, but worth every penny. There's still nothing that touches it.