[eigenket]

It sounds like what you want is scirate. As far as I understand from this post this new thing is just scirate but lacking the interface you're talking about here.

[scarlehoff]

Indeed. Scirate (I didn't know about it) looks exactly like that.

Sadly, the last comments in HEP are more than 2 years old (which explains why I had never heard about it, it seems it never gained any traction)