There are many excellent sites on steam, models, railways, etc on the internet.
The following are those that I use or which have particularly useful information.
SOFTWARE.
There are several programmes on valve gears, probably the best known, and the one with the greatest variety of gears, is by Charles Dockstader., which is available HERE or HERE.
Bill Hall wrote a suite of programmes on valve gear, cylinders, boilers, and much more. They can be found on the Model Engineering site, which is also the host to the lost models directory as well as containing useful information and links to other sites. It is also the entry to the Model Engineering discussion list.
CAD. There are many CAD programmes available. One well-known CAD programme which is available for nothing is Turbocad, the 2D version of which can be downloaded from IMSI (Turbocad).
Screensavers. If you want a railway screensaver, I can highly recommend the one by Mark Goodspeed, which is based on UK railways and has a lot of variety in it. One can even recognise some of the locations. Mark Goodspeed's Railway Screensaver.
Conversions. There are many unit conversion programmes. I like this one which is free and has loads of useful conversions, even US to UK measures, and such things as slugs per hour if your interest is gardening. ideal, especially if you want to know how many Parsecs are in a Roman Mile. ESB unit conversions.
If you need to convert currencies, then THE programme to download is the Currency Converter by Alex Belgraver. It can easily be updated to show all the latest rates, which are updated several times daily. It can be found HERE.
There are several places on the Internet for those interested in steam, trains, model engineering, and all other aspects of these hobbies, to interact and exchange information.
There are a number of groups on Yahoo, which are sources of information on various aspects of the hobby.
The two largest model engineering discussion lists are:
