Houdini Indie does permit export. The free version does not. Indie costs 200USD/year.
Houdini is probably the most powerful 3D application available. This isn’t to say that Houdini is the best tool for everything, it isn’t. But you can do about anything with Houdini, including building your own solvers from scratch using the out-of-box tools provided, without having to use the SDK.
It’s a bit faster than Realflow, and offers a lot more, even within fluid simulations. That said, it’s not easy and it’s definitely not for everyone. I would encourage you to give a solid three months with the free version before buying a license. Even with the rendering restrictions, there’s still plenty to do with Houdini. Most of my personal projects and tinkering I don’t even bother rendering. The process of building tools and sims is rewarding in it’s own right.
But give it a an honest go, and don’t be too intimidated. Over time houdini will make sense if you have the patience and time to dedicate yourself.