The aim of this book is to help people to get started with Gnucap. Gnucap is an open-source circuit simulator, or circuit analysis package (in short: CAP). This book can also be read online at gitbooks
There are other places where you can learn about Gnucap such as:
the gnucap wiki: http://www.gnucap.org/dokuwiki/doku.php?id=gnucap:start
The wiki for Gnucap examples and tuorials
The Gnucap help mailing list: https://lists.gnu.org/archive/html/help-gnucap/
However, these resources require certain prior knowledge of EDA software tools such as SPICE or stop at questions of running your own simulation flow from start to end. This Gitbook tries to help with that aspects of electrical circuit simulations.
Also, if you want to get an overview from the Gnucap developers, there are nice talks on Gnucap in FOSDEM conference talks:
The main Gnucap project page can be found at the GNU servers. Note, Gnucap has been around for a long time, and not information is up to date, for the latest developments you should track changes on the Gnucap source code.