See has a number of unique features, such as saving mark-up for viewed files while leaving them unaltered. Document "meta-data" is maintained independently for each user and loaded automatically, allowing you to keep bookmarks and highlights for read-only system files (including man pages) in a simple and intuitive manner. See also does layered finds, regular expression searches, hyper-linked apropos searches, and can be set to monitor an existing file (such as a log) for changes.
See uses it's own local socket server to accept requests from the command-line, allowing easy integration with file browsers and other software. There's also cross application drag n' drop support, and handy little features that allow you to view the output of shell commands and process the text buffer with an external command (sed, awk, grep, perl, etc.)

See looks nice, takes up a minimum of space and has two gently blinking "toggle lights" on the interface to control the server and file watches.

See is POSIX compliant.