Amateur

From the Latin "amator", meaning "lover". An amateur is someone who does his work for the love of it, not for recompense. Often used as a derogative term by people who are more heavily invested in their own formal credentials than they are in the work.

Amateurs sometimes do the best work in their fields. The Linux OS is the standout example. Developed mostly by amateurs (some of whom blur the line between amateur and professional by contriving to get paid), it's far superior to Microsoft Windows on just about every metric.