SPICE OnlineThe following links contain general information about SPICE and NGSPICE.
General SPICE pages
Berkeley Spice Page
This page has spice3f manuals and information as well as information about nutmeg, an interactive plotting tool that is often used with SPICE.
The Spice3f5 documentation, hosted here at ngspice.com for your convenience.
Free versions of SPICE
EasyEDA is a free, cloud-based EDA suite, integrating Schematic Capture, Circuit Simulation using ngspice and PCB layout in a web browser GUI. Work can be kept private, shared or made public. Schematics and libraries can be imported from Altium, Eagle, KiCad and LTspice. Files can be exported in a number of formats including JSON. Low cost PCB fabrication is also offered as an option.
Powerful schematic capture and SPICE simulation all from a web browser!
Good version of SPICE for Windows, but some limitations in the free version.
Similar to WinSpice, but for Mac. No limitations on functionality.
NGSPICE at SourceForge
The official development site for NGSPICE.
PDF ngspice manual
NGSPICE files available here for your convenience.
Other circuit related sites
Schematics are the language of electronics. They provide a concise and comprehensive diagrammatic description of a circuit. Schematics.com allows users to connect and share designs and ideas in a like-minded community.
The MOSIS Service
Low cost fabrication of integrated circuits.
Jacob Baker's educational circuit design website