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.
Multixterm creates multiple xterms that can be driven together or separately. It can be used to login via SSH to multiple hosts and control them simultaneously, or for ad hoc things where you want to see the results as you type. Each xterm may also be driven separately. Multixterm is scriptable so that you can easily fire up, for example, a dozen xterms with a single command, tiled nicely on your screen. In addition to SSH, multixterm can drive rlogin, telnet, passwd, or any program that runs in an xterm.
ggiterm is a software terminal emulator like xterm. However instead of X, it uses the GGI system for its rendering, which allows it to be displayed on anything from a framebuffer to multi-screens across networked hosts (including ordinary X sessions). It features multiple font formats, anti-aliasing, vt100 compatibility, and full internationalization.
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.
ROTE is a simple C library for VT102 terminal emulation. It allows the programmer to set up virtual 'screens' and send them data. The virtual screens will emulate the behavior of a VT102 terminal, interpreting escape sequences, control characters and such. The library supports ncurses as well so that you may render the virtual screen to the real screen when you need to.
JChassis TermUI is an API for simple GUI-like user interfaces on ANSI/VT100-compliant terminals and terminal emulators, such as Linux virtual terminals, GNOME Terminal, and KDE Konsole. The intent is similar to that of the ncurses library, but done in pure Java. Several commonly used widgets are available.
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.