A set of 12 universal POS tags described in A Universal Part-of-Speech Tagset by Slav Petrov, Dipanjan Das and Ryan McDonald (2012) In Proceedings of the Eight International Conference on Language Resources and Evaluation (LREC'12) (code and mappings available: here.

Tag	Meaning	English Examples
ADJ	adjective	new, good, high, special, big, local
ADP	adposition	on, of, at, with, by, into, under
ADV	adverb	really, already, still, early, now
CONJ	conjunction	and, or, but, if, while, although
DET	determiner, article	the, a, some, most, every, no, which
NOUN	noun	year, home, costs, time, Africa
NUM	numeral	twenty-four, fourth, 1991, 14:24
PRT	particle	at, on, out, over per, that, up, with
PRON	pronoun	he, their, her, its, my, I, us
VERB	verb	is, say, told, given, playing, would
.	punctuation marks	. , ; !
X	other	ersatz, esprit, dunno, gr8, univeristy

Table adapted from the NLTK book (Chapter 5).