So, how does this compare to ohai (from Chef) and mcollective (from Puppet)?

Is there a packaged version for other OSes, or is this Red Hat/rpm only?

The tar.gz package is compatible with RedHat and Debian OS based, CollectNode is a portable software, so all the requirements are already packaged (except the samba-client package, only required if you are going to work with Windows systems.)

so far, you can download the tar.gz or rpm package, a .deb package will come eventually. CollectNode doesn't required any client installation, so is not required to install the client package as mcollective requires, and any way, collectNode is very focused on the report, making very useful to get a global view about you want to know easily.

A quick glance at the documentation would seem to indicate that this is very similar to Ansible or any of the other major configuration management tools (Chef, Puppet etc). I'm not quite sure why you would use this over one of those.

When I need to know which servers have an specific parameter in a file (for instance), and get a report sorted by operating system and server name, not displaying the servers where the file doesn't exit, I wouldn't use Ansible, I would use CollectNode. It is the perfect complement for Ansible. The big point of CollectNode is that is very quick and very focused on reports, making very easy take the information wanted with the format best fits your necessities.