Throughout history, people have tried very hard to come up with "constructed languages" that would become Earth Standard languages, spoken universally. None have been as popular as natural languages are, and they mostly seem to be falling into obscurity. Before they go, we'll do a survey of humanity's greatest attempts to overcome the power of Babel.
If you're reading this, in a way you're very lucky. English is spoken as either a first or second languages by anywhere between 800 million and 1.8 billion people on Earth. This means that you'll be able to communicate with a good part of the world's population. An alternate view is that you're very unlucky. If you're a native speaker you're not that likely to have learned a second language. English has become a candidate for the modern lingua franca not because it has the greatest number of native speakers, but because the greatest number of non-native speakers are willing to pick it up. It has occurred to native and non-native speakers alike that this might not be fair. The pushiness - and ultimate temporariness - of dominant languages has caused people to try to come up with a simple, common language that the entire world might learn to allow for basic communication everywhere. The languages have, for the most part, died on the vine. But let's look at their noble attempts to unite the world.
Solresol
Solresol was a forty-nine year labor of love, and the first widely spoken constructed universal language. It was conceived in 1817 by François Sudre and continued to be both taught and refined by his followers until two years after his death in 1864. Sudre wanted to be practical about his universal language. Solresol was created to be very basic - a street language that would help people around the world resolve everyday interactions. He also didn't want to give any speakers of any language an advantage, and so based his language phonetics on musical tones.
The syllables consisted of the do re mi fa sol la si scale that is much like the one we know through The Sound of Music. Just like the song in The Sound of Music, people can put the syllables together can form words and phrases. Because the syllables are so few, Solresol speakers can signify each one by marks on a musical scale, different colors, hand gestures, numbers, or very basic lines on a page. So, for example re-si-mi-re is brother. I could write that with a musical score. I could write it by writing the number 2732. I could write it by using crayons and making lines of orange-pink-yellow-orange. Because of its straightforward rules and the ease with which it could be signed with hand gestures, it picked up some popularity. However, other constructed languages supplanted it, and now the only place you're likely to see Solresol is on obscure internet communities.
Esperanto
This was one of the languages that pushed Solresol aside. It made its debut in 1887, the brain-child of Ludovic Zamenhof, a Polish physician. Zamenhof, who was troubled by the language-based conflicts he saw in his homeland, first wanted to reintroduce Latin or Greek, but he found their idiosyncrasies frustrating. After looking into a few languages, he identified stumbling blocks - irregular verbs, unusual spelling, gendered nouns - and created a languages that eschewed all of the messiness of the natural. Esperanto is phonetic, regular, and grammatically simple. In some ways the negative reaction to the idea of Esperanto fueled its growth. The Russian Czar had dreams of an earthly tower of Babel and banned the learning of it by his people. Eastern Europe and China, wary of the growth of English, saw Esperanto as a way to promote a common language that didn't favor any particular nation. Ironically, the language meant to unite everyone got its first kick due to the politics of resentment. Its peace-and-love spirit wasn't embraced in English-speaking countries until, of course, the 1970s.
Although it's, by far, the most popular auxiliary language, Esperanto has proved impractical. Since it's nobody's native tongue, it relies on people's willingness to learn it as a second language. Few people are motivated to do that unless there are already a great deal of people also willing to learn it, and so it seems to be spiraling down, not up. One good kick from people around the world and it might yet become a common language, but to do that it has to overcome its homegrown demons.
Ido and its Associates
The first Esperantido, as Esperanto offshoots are called, was Mundolingo. It sprang up eleven years after Esperanto was introduced. Over the years there have been at least two more Esperantidos, the most popular of which was Ido. Ido got its own dissenting offshoot, Adjuvilo. Languages thought up by idealists face all the challenges the that natural languages face, as well as all the challenges that idealists face - all of its adherents are sometimes more committed to ideals than to compromise. The result? Schism, schism, schism. Ido, funnily enough, was most loyal to Zamenhof's vision. It was he who first proposed the changes to make Esperanto simpler a few years after he debuted it. Regular speakers were slow to adopt the changes, and so Ido has become a dialect of the larger Esperanto.
Occidental
Occidental came from a member of the profession that is historically most known for learning many languages - sailors. A crew of almost any ship had to cobble together common bits of languages to be understood. Edgar von Wahl was a naval officer who didn't want to create a language that people would necessarily learn. He wanted to create a language that a large group of people would already speak. Anyone who has studied Romance languages has noticed that certain words in other languages are similar to their own and so comprehensible to them. Wahl put those shared words together in a regular way that, ideally, would be understood by any person who spoke any romance language. Many non-speakers say that they are able to understand the general jist of anything said to them in Occidental, even if they haven't studied it.
Afrihili
Most "universal" languages are European in origin. They may be easy for people who come from Western Europe, but people who have no language connection have a harder time learning them. Afrihili was an attempt by Kumi Attobrah, a historian, to create a universal language that came from Swahili and African languages. The language, invented in 1970, used the Latin alphabet, but added two extra vowels. All the vowels were then put on a "vowel triangle," with vowels at each apex and along each side. To change an adjective to a verb, a person would swap the vowel at one corner of the triangle for a vowel on another corner. While there are books on and websites in Afrihili, it is not widely spoken anywhere.
Sambahsa-Mundialect
This is the latest attempt at an artificially-created international language. The language, released in 2007, blends European languages with Arabic, Chinese, Turkish, and Indonesian. It represents, among other things, a break from the strict phonetics of Esperanto-type languages. There are multiple sounds that can be made with one letter. It's an attempt to make a new Indo-European language, and tries, at all times, to use words that are common to at least two different languages. Since it's only been around for five years, there aren't too many adherents. But you could be the next!
Via Omniglot twice, NCBI, Is That a Fish In Your Ear, and Sambahsa PBworks.