Embedded script languages for PHP?

I've not seens many engines that allow another scripting language to be enabled in PHP :-(
Even on PECL, there doesn't seem to be lots of entries (see the "languages" category, for instance : only one, which you already know)
And on PEAR, I don't even find anything that would match your criteria...

I've played with Spidermonkey a bit (see this article on my blog, in french), and it's kinda fun, yes. But it was not really stable a couple of months ago when I wrote that article -- and there have only been a few commits since. So, I understand why hosting companies would not provide it on their servers...
Even if I'd like them to : could be great to allow non-PHP developpers to develop scripts for your application !

A question though : why do you want/need another language than PHP ?

What I mean is PHP is already installed on your server, you obvisously have experience with it, and it's a quite powerful language... So why do you want/need to work with something else ?

Using PHP's eval, you can even think about executing "dynamic" PHP code (Yep, eval is eval and all that, I know ^^ )

Another option, using stuff like "exec" and the like would be, if you are on a Linux server, to launch some kind of shell-script ; but I would definitly prefer coding in PHP than shell, and I'm certainly not the only one ^^

Anyway, keeping an eye on the answers you might get, which could interest me quite a bit too ;-)

I understand your concern. Even for trusted sources, PHP provides more access than is necessary to the whole environment of the web request. Even if the scripters are trusted and even if they can only harm themselves with a scripting error, a more constrained scripting environment would be easier for them to use and easier for you to support.

You want something that can be sandboxed off, that can only access resources you explicitly assign to its scope, and that executes in a "play within a play" runtime environment rather than in PHP's own.

One approach is to use a web templating language for user-submitted scripts. These provide a certain amount of control (variable assignment for example), and close off other options, for example you can't write an infinite loop. I've used Velocity for this purpose in Java applications; I think something like Smarty might work in PHP, but I don't have direct experience of using it for that purpose.

Another approach, if what the scripts are required to do is constrained by the domain, is to implement a Domain Specific Language (DSL). I mentioned that in this answer.

Apart from that, I don't know of any pure-PHP implementations of scripting languages. It's something I'd be interested in myself.