Not quite behavioral (which is a very specific thing), but Eve was certainly synchronous. It was one of the two languages (the other being Céu) that brought syn

Not quite behavioral (which is a very specific thing), but Eve was certainly synchronous. It was one of the two languages (the other being Céu) that brought synchronous programming from the niche of safety-critical realtime systems to more mainstream software. IMO, it was the most theoretically-advanced programming language around.