T-gauge model railroad layouts are models of standard-gauge railroads at a 1/450 scale.

 This means that everything in a T-gauge layout is 1/450th the size of its real-world equivalent - which is very small.  The T-scale trains are produced by a Japanese company named Eishindo... which also produces 1/450 scale train tracks, people, boats, buildings, and animals as scenery to accompany their miniscule model trains.

 The only way a model railroad can usually be built any smaller than T-scale is to use drive belts powered by electronics underneath the layout.  This is the technique used to make TY-scale (1:900)and other novelty hand-made scales smaller than T-scale, possible. 

T-scale is, despite the presence of these smaller scales, the smallest 'real' model railroading scale currently available... the smallest scale that uses stationary track and electronics inside the trains themselves.

Although it remains a niche scale, and in some purists' minds, a novelty scale rather than a "Real" model railroading scale, it has a steadily growing foothold in the model railroading community, and a rapidly growing number of available products.  It is gaining ground over time.  Eishindo continues to produce new T-scale products, and there are also a growing number of miniature cars, aircraft, and airport scenery items being produced by Herpa in 1/400th and 1/500th scale for model airplane enthusiasts.

 These scales are close enough to T-scale that they are effectively interchangeable, so it's not unusual to see connections between model-railroaders and other model-builders working with model aircraft or model ships.  The three hobbies can be blended to form complex and interesting layouts featuring various types of transportation - planes, trains, ships, cars, and trucks are all possible at this scale, as are trees, fences, people, farm animals, and buildings - and the finely ground clumps of foam foliage and powdered grass, plaster, water gel, paints, etc, that are used in Z-scale layouts work just as well in T-scale.

1:500 scale is also sometimes used in large-scale architectural and urban planning models; this allows absolutely massive objects to be represented in miniature without consuming an umanageable amount of space.  At this scale, an entire square mile of real-world terrain can be represented in an 11 by 11 foot space. 

This means that spaces such as Vatican City or Disneyland could accurately be depicted on a tabletop at this scale.  T scale is small enough to make models practical which would consume enormous amounts of space in any other scale; for instance skyscrapers, ocean liners, and airports... In T, the Empire State building would be only about 3' tall... and the lower half of Manhattan could be accurately represented, each and every building, in a room of, say, 25' by 50'... 25 by 50 feet.

One final possible use for these tiny scales is for construction of a model of a model railroad layout... a T-scale model can be inserted into a 1/12 scale dollhouse as a doll's approximation of the common O-scale.

Adding up the total number of web pages related to " T gauge" and " T scale" on Google indicates that over 400,000 web pages now mention this modeling scale...

By comparison, a similar search for " HO gauge" and " HO scale" produces around 2,200,000 results... suggesting that as of this year, 2011, T-scale is now 1/5 as popular on the internet as HO-scale, and more popular than TT or Z!

Now, granted, these results are skewed; not every model railroader uses the internet or has a webpage, so these figures do not accurately reflect the total model railroading population.  Nonetheless, they are an indicator worth considering.