u-blox's free (proprietary) evaluation and configuration software for u-blox receivers. Connects over the serial/USB port and shows the raw NMEA and binary UBX messages, satellite view, signal levels and the live fix, and lets you reconfigure the receiver. The go-to GUI for inspecting exactly what a u-blox module is reporting; Windows-native (u-center 2 for newer modules).
Lifecycle not assessed: nobody has checked yet whether this tool is still maintained, sold or working. Check the project's own page before relying on it.