MathJaxTM is an open source, Ajax-based math display solution designed with a goal of consolidating advances in many web technologies in a single definitive math-on-the-web platform supporting all major browsers.
Xournal is an application for notetaking, sketching, keeping a journal using a stylus. It is free software (GNU GPL) and runs on Linux (recent distributions) and other GTK+/Gnome platforms.
TinyMCE is a platform independent web based JavaScript HTML WYSIWYG editor control released as Open Source under LGPL by Moxiecode Systems AB. It has the ability to convert HTML TEXTAREA fields or other HTML elements to editor instances.
SaVi - satellite constellation visualization. Simulate Iridium, Globalstar, Sirius, GPS, Teledesic and other systems, modify them, or design your own. Uses Tcl/Tk and Unix libraries; 3D viewing option requires Geomview running on X Window. BSD license.
OpenSource GPS is software for x86 PCs that allows you to acquire, track and demodulate signals from GPS satellites. OSGPS requires a Zarlink GP2021 12 channel GPS correlator chip or software receiver hardware such as the GPS1A, see www.gpscreations.com. Does not appear to be very active recently.