The bundle splits txfonts.sty (from the TX fonts distribution)
into two independent packages, newtxtext.sty and newtxmath.sty,
each with fixes and enhancements. newtxmath's metrics have been
re-evaluated to provide a less tight appearance, and to provide
a libertine option that substitutes Libertine italic and Greek
letter for the existing math italic and Greek glyphs, making a
mathematics package that matches Libertine text quite well.
newtxmath can also use the maths italic font provided with the
garamondx package, thus offering a garamond-alike
text-with-maths combination.