The software development industry is filled with folks who are full-time or part-time consultants and contractors. I had been doing part-time consulting work for years until it eventually blossomed into a full-time job.
Most developers are perfectly happy (and busy!) with their day job and are not doing any kind of consulting work. That said, the sheer number of folks who are consulting in addition to or in lieu of a full time job is pretty amazing to me.
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