rxvt-unicode is a clone of the well known terminal emulator rxvt, modified to store text in Unicode and to use locale-correct input and output. It also supports mixing multiple fonts at the same time, including Xft fonts, real transparency, and an optional embedded Perl interpreter that allows you to extend your terminal easily.
FbTerm is a fast terminal emulator for Linux that uses the frame buffer. It is mostly as fast as the Linux kernel's terminal when accelerated scrolling is enabled on the frame buffer device. It allows you to select fonts with fontconfig, auto-detect and convert text encoding with support for double width scripts like Chinese and Japanese etc, dynamically create and destroy up to 10 windows, record scroll-back history for every window, and copy/paste selected text between windows with mouse the when the gpm server is running.
Libptytty is a small library that offers pseudo-TTY management in an OS-independent way. It was created out of frustration over the many differences of PTY/TTY handling in different operating systems for use inside "rxvt-unicode". It also offers session database support (utmp and optional wtmp/lastlog updates for login shells) and supports forking a proxy process after startup and dropping privileges in the calling process. It offers C++ and C-only APIs.
xremote is a simple tool that lets you grab the mouse and keyboard of another machine and control them with your local mouse and keyboard. It creates a form of remote control of other machines. All mouse- and keyboard-actions on the local machine are forwarded to the remote display.
QuadKonsole is a terminal application that embeds Konsole kparts in a grid layout. This saves memory, provides faster startup, and makes it unnecessary to align your Konsole windows by hand. It also provides a lot more screen real estate, makes navigation easier by using arrow keys, and allows all Konsoles to minimized or maximized at once. It only occupies one slot in the taskbar.