Online applications

I'm trying to learn more about online applications and whether there may be a source (just like a download.com etc) that offers generic software that can be implemented from within a web site.

I would imagine that these programs are probably custom developed?

Take for example, this site and their "Maestro" drawing software.

That is really what I'm after but something simpler -- a drawing tool with the basics (rectangles, fonts etc) -- that I could put on my web site.

Is there a web site for example that specialzes in online tools that you simply download and install somehow?

(Dream on, no doubt).