Esperanto
Esperanto is a constructed (or 'artificial') language created by L.L. Zamenhof in the 1870s and 1880s. Zamenhof envisaged Esperanto as an artificial lingua franca that would facilitate easier global communication. Despite this, he chose to derive much of its vocabulary from Romance and other Indo-European language families such as Germanic and Slavic.
Ido is a constructed language which has been derived from Esperanto.
Grammar
The Esperanto grammar is very simple. For example, there is only one conjugated form of the verb and no grammatical gender, so all nouns have the same article (la). All nouns end in -o in the subject form and in -on in the object form, while all adjectives end in -a (subject form) or in -an (object form). Moreover, most antonyms of a word are formed just by adding the prefix mal- to the original word. So nova means for example "new", while malnova means old.
Use
Today, the users of the languages number at least in the tens of thousands, of whom a few have been identified as native speakers. However, the dominance of several natural languages in the world, especially English, has meant that Esperanto is yet to emerge as a true global tongue.
For Esperanto speakers there are several international organizations, of which the Universal Esperanto Association is the most important. Moreover, there also exists literature and music in Esperanto as well as Esperanto radio stations.