Kimpanel is a DBus-based User Interface for Fcitx. It's oriented from KDE, and now it can also support gnome-shell.
Since 4.2.0, Fcitx will have ability to automatically switch to different UI based on current environment at runtime. If you are using Fcitx 4.1, you can use
fcitx -u fcitx-kimpanel-ui
to force fcitx to use kimpanel.
You need a kimpanel frontend to actually use kimpanel to display UI, currently there are several implementations list below.