Tomy, a company originally formed as Tomiyama in Japan in 1924, was incorporated as Tomy Kogyo Co., Ltd. in 1963. In 2006, Tomy, by then the second-largest toy manufacturer in Japan, merged with Takara, the neighboring third-largest toy manufacturer that started in 1955. The resulting Takara Tomy Co., Ltd. is referred to as "Takara Tomy" in Japan, where both names carry recognition value, and simply as "Tomy" in the rest of the world.
Tomy largely produces a wide range of toys for young children and baby supplies. It has grown to include many subsidiary companies, including sales offices and factories in outside countries. One subsidiary, Tomytec Co., Ltd., produces model railway products (among other products) under its own name, and also manages Tomy's "Tomix" product brand for model railroad products. Tomy offered its first N-gauge locomotives and cars under the "Tomy" name a few years before creating the "Tomix" brand name in 1976. The word "Tomix" is always shown in English characters, since it does not directly translate into Japanese. In very general terms, the Tomix-branded line contains on-going products, while the Tomytec line consists of one-time, limited-production products.
Compatibility of Tomix and Tomytec products with other N and HO trains N-gauge is N-gauge, defined as nine ("N") millimeters between the tops of the two rails. Tomix trains will run on other N-gauge track, and other N-gauge trains will run on Tomix track. Slight incompatibilities do exist over the decades, due to varying heights of the metal rails and depths of wheel flanges made by various manufacturers, but in general nearly everything inter-operates. Tomix makes no HO scale track, but their HO trains can run on HO and OO track made by other manufacturers.
This compatibility does not mean other manufacturers' track pieces use the same connection system as Tomix track (or each other's track), or that rolling stock coupler systems are always compatible (they sometimes vary even within one manufacturer's own products).
What's it worth? Take a look at this Tomix price guide: sold listings for a value indication.