The newtx 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 letters for the existing math italic and Greek glyphs, making a mathematics package that matches Libertine text quite well.