LaTeX:

LaTeX manuals, including the particularly recommended (not so) short introduction, available also in Polish.

Information on using BibTeX: in English and in Polish.


Gnuplot:

Gnuplot manuals in the HTML and PDF formats


Fortran:

Fortran 90/95 Programming Manual - a small book

Fortran 90 Handbook - a large book


GSL:

Manual for the GSL library in the HTML and PDF formats


Netlib:

Numerical procedures (mainly in Fortran): www.netlib.org