HTML mixed with code in the same file? A new language? A new database? What makes an app written in opa better than a PHP codebase where HTML is mixed with PHP all over?
This opa project doesn't look like such a big deal to me. It just limits freedom too much from what I can see.
Build something like this which merges the HTML with some weird looking code and you've wasted quite some time for nothing.
Wt has been around for a while with an approach not far from this one and I never stopped thinking it's one major piece of junk.
To the guy who posted this link for SEO purposes:
I'll make sure to block that site from my browsers, it's 100% trash.
This is the relevant link: http://opalang.org/