Charlie Hawkins emailed to tell us about a new science & engineering encyclopedia called DiracDelta*. It is completely free to use, as one would hope, given the existence of Wikipedia, and they update their database on a daily basis. A new version appears monthly, which is more than you can say about good-old paper encyclopedia’s of course. Currently, there are about 5000 pages, some of which have more detail than others, but Hawkins emphasises that this is a work in progress and always will be.
One of the most interesting aspects of DD is not the encyclopedic entries themselves, but the various applets including a clipboard and calculator that allow readers to work more interactively with the data presented. Moreover, there is a whole stack of scientific tools that allow you to input values directly and work out everything from aerodynamic drag coefficients to signal processing bandwidths by way of decibels, fuel consumption, and moments of inertia.
*No relation to AlphaGalileo as far as I know!