A free cross-platform library of fast C++ routines for plotting data in up to 3 dimensions. It can export plots to bitmaps and vector EPS, SVG, IDTF files. There are simple window interfaces based on GLUT, FLTK and/or Qt. MathGL can also be used in the console. There are interfaces to a set of languages, such as, C, Fortran, Pascal, Forth, Python, Octave.

These packages are either mandated by the core LaTeX team, or very widely used and strongly recommended in practice.

Uim is an input method module library which supports various scripts and can act as a front end for a range of input methods, including Anthy, Canna, or SKK (for Japanese), Pinyin (for Chinese), Byeoru (for Korean), and M17n (for many other languages). Most of its functions are implemented in Scheme, so it's very simple and flexible.

Calibre is a complete e-library solution. It includes library management, format conversion, news feeds to e-book conversion, e-book viewer and editor, and e-book reader sync features.

Bauble is a software application to help you manage a collection of botanical specimens. It is intended to be used by botanic gardens, herbaria, arboreta, etc. to manage their collection information. It is a open, free, cross-platform alternative to BG-Base and similar software.