Many years ago I read that Arabic bore signs of being a constructed language. I had wondered an 'esperanto' based on Semitic rather than European languages could be devised. Apparently yes - its name was Balaibalan, rather a nice name, I think. Little is known about it, but here's a wiki article:
http://en.wikipedia.org/wiki/Balaibalan

It would be interesting to know whether a semitic constructed language would be easier to learn than E-o, for people without relevant backgrounds for either. The trouble is that any attempt at comparison would be confounded by the world-wide prevalence of English as a second or professional language.

Except that it is based on Arabic, Turkish, and Persian, and of those, only Arabic is Semitic. So I wouldn't really call it a semitic planned language, but its existence is interesting nonetheless (and also the fact that the source languages come from three completely different language families - Semitic, Turkic, and Indo-European. I wonder which language family the grammar followed?)

erinja:I wonder which language family the grammar followed?)

The wiki article says 'simplified Arabic', perhaps a semitic version of Latino sine flexione.
But it appears to have been devised by a mystical sect for its own purposes, and so might be less suitable as an all-purpose language which E-o is intended to be.

In Cuba exists a secret society called “Abakuá” founded in the XIX century by African slaves from the Calabar region of Nigeria. The languages of the original founders were closely related and were somehow blended together (for ritual and practical purposes) into a new phonetically hispanized and grammatically simplified secret jargon. The predominant vocabulary is of Efik origin, but many words and expressions were also borrowed from other African languages. I’ve had the chance to listen to the language 3 or 4 times in my life and it sounds totally alien and cryptic. When the “abakuás” or “ñáñigos” pray or chant they use very rigid ancient “formulas” that are sufficiently grammatically correct to be recognized (by native speakers) as horribly pronounced Efik. Out of the rituals and ceremonies they use a much more hispanized jargon… but, believe me, absolutely incomprehensible.