|SPICE simulators will allow you to check out your designs on the PC,
before committing the design to the breadboard or prototype stage:||Aimspice - download a student version from their
site.||Anasoft - Schematics entry integrated with industry standard SPICE 3f5 engine, the demo which can be downloaded from the website seems to work well. Full version requires license key to unlock the demo, c. $50, although as Kevin points out, this is free at the moment and will be for some time. Your own symbols and components can be added via the symbol editor. (Modified 27/5/2000).||Beige Bag have a neat looking integrated simulator on their site, with a 30 day fully functional trial version. Lots of models too... Check it out!||Circuit Designer Pro - A very neat integrated package with PCB autorouter. Demo is functional for 45 days, but will not save or print. Also contains some vacuum tube models which drop straight on, and an example of a vacuum tube power amp. [6MB].||Eagle schematics and PCB layout. This is not a simulator, but a schematic capture and routing tool which I understand can integrate with SPICE. Includes auto-routing facility, and a large library of components. Hobbyists edition available for non-commercial use, free of charge with a maximum board size of 100mm x 80mm with two layers. EAGLE runs on Windows® 95, Windows NT®, OS/2® Warp and MS-DOS®, and registered editions start at $49 which includes telephone tech support. (Added 20/1/2000)||Electronic Workbench. Very easy to use with package scaling for Personal, Student and Pro versions. Uses real world DMM's and Scopes to provide results of simulations. Integrated PCB placement software now available too.||Intusoft, with their integrated simulator - Ispice. Another big production with a few restrictions on use. Also host the excellent MAGDEMO transformer design software, and a host of useful newsletters on SPICE modelling.||LTSpice/SwitcherCAD III - a nice easy to use simulator which is gaining rapid acceptance. There's a page on how to use it with the vacuum tube models here. (Added 5/4/2003)||MicroCap 5 - Costs $3,495 although a student/demo version is available for download [1.75MB].||Orcad, the makes of Pspice integrated schematic capture, simulation, and PCB routing suite. All of their tools are available on a CD which is sent free on request - this is a fully working suite limited to 60 components and some restrictions on the libraries (altered 13/1/99).||SIMetrix - A UK developed simulator with schematic capture linked to spice 3.x. You can download an almost fully functional demo, limited to 120 nodes (8 megs in size). (Updated 05/11/2003).||Tina - "TINA PRO is a powerful yet affordable software package for designing, simulating, and analyzing analog, digital and mixed electronic circuits". Demo available for download (Added 22/7/2002).||TopSpice by Penzar. "An affordable integrated computer-aided circuit design software package offering advanced native mixed-mode mixed-signal analog/digital/behavioral simulation based on the industry standard SPICE program." More news when I've checked their demo out (2mb).||Winspice3 by Mike Smith. An excellent port to Windows 95/NT of the traditional SPICE 3f4 engine. Now enhanced to handle some of the 2g6 specific statements. (Updated 2/1/2003).|
There is also a good Windows (32 bit)rendition of traditional Berkeley SPICE available from ftp.heise.de/pub/ct/spezial/spice3f4.zip - they have models stored there too.
Try the following page - Terry Pinnell has a much more comprehensive list of ECAD stuff than the list above - http://www.terrypin.dial.pipex.com/ECADList.html