Developer FrankenGraphics has recently updated NEXXT Studio, a tile editor that lets you work with graphics for and in the style of the 8-bit Nintendo Entertainment System, to version 3.1.0. This update features a few more fixes, as well as some new minor additions. Some hotkeys have been changed, and new hotkey combinations have been added. PNG import now supports 1-bit (2-color) files. Works for both canvas (namesheet/map) and tile set imports.
Read the official changelog for details. The new version is available for free download.