DarwinNE

Lapack is 'THE' package for linear algebra applications. At any time you need to solve some non trivial numerical problems involving matrices, you definitely SHOULD have a look at Lapack.
I use it for matrix inversion an manipulation as well as for calculating eigenvalues and eigenvectors of very large non sparse systems and it is just wonderful to use. It can be used along with C or C++ code, despite it is written in Fortran, so once again it deserves to be studied with a lot of respect.

So, all you guys, thanks, thanks, THANKS for all the effort you are putting in this wonderful software.

FidoCad is a small, fast and easy to use Windows editor particularly meant for electronic circuits. Hobbyists can draw very easily schematics as well as PCBs, with a philosophy very similar to the use of the old Letraset decals.
Drawing are represented with a very compact 7 bits text format which can be copy pasted into non-binary Usenet groups, as well as forum messages. Anyone can get the circuit, modify it and repost a modified version. This made FidoCad a widespread choice in the italian Usenet community from late '90s.

The major drawbacks are that FidoCad works only with Microsoft Windows and that all the documentation and the interface is only available in italian.

Atlas can provide a very useful basic automatically tuned linear algebra package when an optimized version of BLAS is not available (or simply too expensive) for the architecture in use.

I am regularly using static checking of the code I write. For C++, I tried cppcheck for a project dedicated to the simulation of electromagnetic field propagation in a structure. I was pleased to see that I was able to compile and run cppcheck in a few minutes. It effectively found a few issues in the code and allowed me to fix it quite rapidly.
Static checking does not allow to find every possible issue, but tools like cppcheck are definitely worth using, in conjunction with dynamic test software such as valgrind.