Serial Terminal Emulator on Linux/Ubuntu

Minicom, PuTTY, picocom, gtkterm, or cutecom

Console based:

1. minicom: the grand master and the one most people use
2. picocom: a mini minicom
3. some others not very well used such as: microcom, nanocom

GUI based:
1. cutecom (Qt based), able to dispaly and send HEX
2. gtkterm (GTK based, last release 2005), able to set serial port pin, and read pin status, and display and send HEX
3. PUTTY for linux (GTK based)

I recommend minicom, picocom and gtkterm.