tcpdump prints a description of the contents of packets on a network interface which match a given boolean expression. It can also be run with the -w flag, which causes it to save the packet data to a file for later analysis, and/or with the -r flag, which causes it to read from a saved packet file rather than to read packets from a network interface. In all cases, only packets which match the expression will be processed by tcpdump. tcpdump logs more than just TCP, IP, or ethernet packets, but has a whole suite of decoders, including ones for USB.
dnscrypt-proxy acts as a DNS proxy between a regular client, like a DNS cache or an operating system stub resolver, and a DNSCrypt-aware resolver, like OpenDNS. The DNSCrypt protocol focuses on securing communications between a client and its first-level resolver. While not providing end-to-end security, it protects the local network (which is often the weakest link in the chain) against man-in-the-middle attacks. It also provides some confidentiality to DNS queries.
SYINF shows in brief a system's CPU brand and model, RAM size, disk space, operating system, regional parameters, and current date and time. It can run in interactive (menu) or batch mode. There are two versions, in the C and C++ languages. They have been tested on 20 (15) compilers, 26 (25) operating systems, and 18 architectures. (Figures in parentheses are for the C++ version.) Both versions are conveyed in source code form only, each as a single ~35 KB source text file.