You're right.
Most, possibly all, hosters don't provide Node.js as part of their
hosted service. If they did, it would work and maybe you can find a
hoster that does. Otherwise, you need a situation where you can get
command line access and install Node.js yourself and keep it running
as a daemon. A VPS or dedicated server should allow you to do that.
I don't have any first hand knowledge on Ajax IM 4.0a. But I do
recall a bunch of exchanges on the Ajax IM Google Group that said that
PHP doesn't work and the maintainer saying, "Yes, it doesn't work and
we aren't planning on supporting it anymore." As I recall, the
distributions on the Ajax IM web site are horribly outdated; you need
to go to their repository and get the latest code from there.
ajaxim 3.41 is the last release for the Ajax IM 4.0a team before they
junked the code base and rewrote everything from scratch using
Node.js. ajaximrpg 3.41 was a fork of ajaxim 3.41 that just had the
names changed. ajaximrpg 4.00 is an upgrade of the ajaximrpg 3.41
codebase with a bunch of new features and bug fixes. It is oriented
towards role-playing games but I'm trying to keep it functional (via
configuration options) for all other uses as well. ajaximrpg 4.00 is
meant to be the inheritor and upgrade to ajaxim 3.41, what ajaxim 3.41
would have been if the original maintainers had continued on with it.
As I recall, new featuers in 4.00 are (1) having an optional lobby so
accounts are optional; (2) registering for a new account automatically
logs you in; (3) whispers; (4) chat logs; (5) rolling dice; (6)
installation can be done on the main page via a wizard instead of on
install.php.