glTron is a tron-like lightcycle game with a nice 3D perspective. 3D acceleration is recommended.

Psi is a cross-platform powerful XMPP client designed for experienced users. User interface of program is very flexible in customization. For example, there are "multi windows" and "all in one" modes, support of different iconsets and themes. Psi supports file sharing and audio/video calls. Security is also a major consideration, and Psi provides it for both client-to-server (TLS) and client-to-client (OpenPGP, OTR, OMEMO) via appropriate plugins.

BlueWho informs and notifies when a new bluetooth device is discovered. Detection can be requested by the user or automatically continuous until it's stopped. A visible and audible notification can be triggered whenever a new device is detected.

SciDAVis is a free interactive application aimed at data analysis and publication-quality plotting. It combines a shallow learning curve and an intuitive, easy-to-use graphical user interface with powerful features such as scriptability and extensibility.

Zyne is a modular synthesizer which comes with more than 10 builtin modules implementing different kind of synthesis engines and provides a simple API to create your own custom modules.

This is the panel provided by the Xfce4 desktop project. If you want a multi-functional panel that can even handle plugins and the like, xfce4-panel might be worth a try.