A tool for editing version-control repository history reposurgeon enables risky operations that version-control systems don't want to let you do, such as editing past comments and metadata and removing commits. It works with any version control system that can export and import git fast-import streams, including git, hg, bzr, CVS, and RCS. It can also read Subversion dump files directly and can thus be used to script production of very high-quality conversions from Subversion to any supported DVCS.

Manual of the GnuTLS (transport layer security) library, which appears to provide a good overview of TLS/SSL.

Circuit simulator with Qt-based GUI.
The Qucs GUI is well advanced and allows setting up schematics and presenting simulation results in various types of diagrams. DC, AC, S-parameter, noise and transient analysis is possible, mathematical equations and use of a subcircuit hierarchy (with parameterised subcircuits) are available. Qucs can also import existing SPICE models for use in your simulations.

Yet another computer algebra system. From the hp museum mailing list.

Links to a number of software oscilloscopes and spectrum analysers.

Hoppi is an application for MacOSX to allow communication with
HP48/49/50 series calculators using the Kermit file transfer protocol.
It supports both USB and RS232 calculator ports.
Hoppi is implemented in Clozure Common Lisp.

Tool to visualise IP traffic or other data collected via SNMP.

musl is lightweight, fast, simple, free libc implementation. It strives to be correct in the sense of standards-conformance and safety and is available under an MIT license.

Collection of software to make NSA's spying more difficult.

PyEphem provides scientific-grade astronomical computations for the Python programming language. Given a date and location on the Earth’s surface, it can compute the positions of the Sun and Moon, of the planets and their moons, and of any asteroids, comets, or earth satellites whose orbital elements the user can provide. Additional functions are provided to compute the angular separation between two objects in the sky, to determine the constellation in which an object lies, and to find the times at which an object rises, transits, and sets on a particular day.

The numerical routines that lie behind PyEphem are those from the wonderful XEphem astronomy application, whose author, Elwood Downey, generously gave permission for us to use them as the basis for PyEphem.