In current-day, common usage the term "dilettante" is taken to mean something negative, signifying a dabbler, someone who takes a superficial interest in artistic endeavor and attempts to somehow pass themselves off as an artist. In the music of the Baroque era, however, the term dilettante had an honorable meaning, identifying a musician whose musical endeavors were not their main source of income. In those times, there were many reasons why a musician would not want to be known as a professional: Tomaso Albinoni (1671-1751), today best known for the famous "Adagio" that he didn't write, listed himself as a dilettante on the front page of his ten published opus numbers, as his day job was working in the family business as a printer of playing cards. Unfortunately for Albinoni, that business ultimately failed, and he was forced to turn pro, becoming an opera coach in his later years.
Music, like acting and some other artistic undertakings, was perceived as being a rather lower class of profession in this era of nobility and landed gentry, and some musicians belonging to the class of nobles opted to take on pseudonyms or to pass their works off under the names of other composers to avoid such association. Count Unico-Wilhelm Van Wassenaer (1692-1766) was a diplomat, Dutch ambassador, and expert composer, yet didn't want to be known for this last attribute. When his six Concerti Armonici was printed by Carlo Riccioti in 1740 under Riccioti's name, Van Wassenaer was probably relieved not to be properly identified; later attributions moved the identity of the composer even farther away to Giovanni Pergolesi's door. Had Van Wassenaer's own instrumental parts not been discovered in Twickel Castle, near Delden, in 1980, his secret might have been safe for good. 
Some recently released recordings have helped to shed some light on other Baroque amateurs with whom we have little or no familiarity. Heinricus Albicastro (ca. 1660-1730) was Swiss by birth, but a Dutchman in most other ways, and unlike Albinoni, seems to have done it the other way around, teaching music and leading an orchestra at the University of Leiden before saddling up as a fearless cavalry officer and serving in the Dutch Army during the waning days of the War of the Spanish Secession. Albicastro, whose Op. 7 Concerti have lately been recorded by Collegium Marianum and Collegium 1704 for Pan Classics, began to publish his works in 1696 and continued to do so until 1706. Though we have lost many of them, surviving works demonstrate the influence of Arcangelo Corelli, but with a highly eccentric twist, in some cases almost sounding like a Baroque Philip Glass. He was made a captain in 1708 and after that, no more music is known.
Another oddball dilettante recently revealed on Le Poème Harmonique's disc Firenze 1616 is Claudio Saracini (1586-?1650) identified as a "Sienese nobleman" in his six publications, of which only five have been found; they date from between 1614 and 1629. Some of his pieces are in such a dissonant style that some scholars have wondered if his compositions weren't compromised by his amateurism, though they seem to be in keeping with the rather bitter and manneristic harmonic style favored by composers that would have been his contemporaries -- Claudio Monteverdi, Don Carlo Gesualdo, Domenico Belli, and Giulio Caccini, among others. There is no record whatsoever of a practicing musician named "Claudio Saracini" in the Venice of his day, and certain of his pieces bear dedications to such heavyweight nobles as Cosimo de Medici and Catherine of Brunswick. The ordinary Italian had no access to such people in those days, and one had to file a petition in order to dedicate printed music to them; the casual nature of Saracini's dedications seem to indicate that he was somehow located within their inner circle. As the name "Claudio Saracini" was such a common one in Siena, this suggests that it might be a pseudonym for another amateur noble who, like Van Wassenaer, didn't want to be recognized for his or her musical undertakings -- perhaps one among the Medicis themselves? Who knows?
The Locatelli Trio - Albinoni: Trattenimenti Armonici, Op. 6 - Sonata No. 11 in A major
Ton Koopman, Amsterdam Baroque Orchestra - Van Wassenaer: Concerto Armonici No. 4 in G major
Collegium Maricanum & Collegium 1704 - Albicastro: Concerto à Quattro No. 3 in C major
Le Poème Harmonique - Saracini: Io moro
