Wireshark is the world's foremost network protocol analyzer, and is the de facto standard across many industries and educational institutions.
Deep inspection of hundreds of protocols, with more being added all the time
Live capture and offline analysis
Standard three-pane packet browser
Multi-platform: Runs on Windows, Linux, OS X, Solaris, FreeBSD, NetBSD, and many others
Captured network data can be browsed via a GUI, or via the TTY-mode TShark utility
The most powerful display filters in the industry
Rich VoIP analysis
Read/write many different capture file formats
Capture files compressed with gzip can be decompressed on the fly
Live data can be read from Ethernet, IEEE 802.11, PPP/HDLC, ATM, Bluetooth, USB, Token Ring, Frame Relay, FDDI, and others (depending on your platfrom)
Decryption support for many protocols, including IPsec, ISAKMP, Kerberos, SNMPv3, SSL/TLS, WEP, and WPA/WPA2
Coloring rules can be applied to the packet list for quick, intuitive analysis
Output can be exported to XML, PostScript®, CSV, or plain text.

MyDefrag (formerly JKDefrag) is a disk defragmenter and optimizer for Windows 2000/2003/XP/Vista/2008/X64. Completely automatic and very easy to use, fast, low overhead, with several optimization strategies, and can handle floppies, USB disks, memory sticks, and anything else that looks like a disk to Windows.