What I mean is, it would be really nice if someone would build such a toolkit - I know the code exists inside things like Chrome and Firefox, but I'm not aware

What I mean is, it would be really nice if someone would build such a toolkit - I know the code exists inside things like Chrome and Firefox, but I'm not aware of any standalone libraries that make it easy to (a) create a sandboxed child process with some code inside it (b) talk to that sandboxed child process (e.g. Firefox and Chrome both have IPC libraries) (c) handle the resulting crashes nicely, restarting child process when necessary