The tech looks reasonably cool, but what is the use case?
EDIT: Your site also makes it sound like it is HTTP(S) only. If it's not, you might want to clarify that.
We often develop sites on our laptops. The more complicated sites are, the more there is to sync around (databases, dependencies to install, version control commits, &c). Showoff is a quick way for us to get feedback from clients or each other without adding overhead to our development process.
p.s. surprised they didn't go for 99 cents
It's possible that they are also pandering to people like me who dislike prices written in that way. I am annoyed by the chore of mentally adding one to every price ending in 99 cents, and I respect sellers who write prices like that less.
ssh -R8000:127.0.0.1:80 my.vps.com
This will forward all connections to http://my.vps.com:8000/ to port 80 on your local machine.
Adjust ports as necessary.
Then you also have the VPS where you can actually host a copy of your app - but that's off-topic.
It's also really nice for testing web hooks or API callback URLs against a local web server (e.g. ecommerce sites with IPN, &c). If you sign up for an unlimited account, you can choose a permanent URL to use for your tunnel (e.g. "my-name.showoff.io").
Working independently on a project or projects with distinct clients who either need or want to give input/feedback on feature development can be greatly alleviated: work up a quick prototype, show off from my local dev machine (never have to touch a server), call/IM my-name.showoff.io, and they get to see it right away, in the same medium they will eventually be using it. This is so much nicer than sending a wireframe or design of a feature.
The long-term benefit is that the my-name.showoff.io URL can be pretty easy to recall & reuse for any number of clients & features.