Word for "things which exist"
Is there a noun that denotes "things which exist"? The only noun form of existence that I can find/think of is "existence" which is the condition of existing, not the things which do.
It's to summarize the tools for a given task that already exist, in a presentation outline (so it needs to be a single word, but I can't give an example sentence!). The other headings are RCA/Techniques/Lacunae.
ETA: Beings implies a certain amount of animacy, which these things definitely don't have.
Solution 1:
Since you are looking for a noun, not an adjective (e.g. extant) or something like "ontology", I suggest either "ens" or "entity".
"Ens" is the noun derived from the Latin verb "esse" (to be); its plural form is "entia".
"Entity" is derived from "entitas" in Medieval Latin, and ultimately from "ens". See also Wikipedia's definition of entity as "something that exists as itself, as a subject or as an object, actually or potentially, concretely or abstractly, physically or not".
Solution 2:
The adjective extant may be relevant, and suitable for a column heading by itself. From en.wiktionary, it means “Still in existence” or “Currently existing; not having disappeared”, etc.
The word entities also is relevant. From en.wiktionary, entity means “That which has a distinct existence as an individual unit” or “An existent something that has the properties of being real, and having a real existence”.
You might also consider terms like stocked, items, things, on hand, tools.
Solution 3:
I would recommend referring to the things you take to exist as an ontology. Within philosophy, "ontology" was originally used to mean "the study of what things exist", but it's now common for it to be used (as a singular noun) to mean "the things which exist". For example:
As for Lewis's own views, with respect to the second question they are fairly unambiguous: He is quite clear that a proper ontology must include not just particulars but also properties and relations...
Source: http://plato.stanford.edu/entries/lewis-metaphysics/
Somewhat similarly (though I know less about this), information scientists apparently use "an ontology" to mean "the things which my computer system takes to exist" (https://en.wikipedia.org/wiki/Ontology_(information_science)).
So in your case, I would have thought that "Ontology" would be an appropriate heading: you are outlining an ontology of tools.