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Variable voltage regulator intended for use with 12V fans typically found in PCs and similar equipment. The design is based on TI's reference design, see http://www.ti.com/lit/ds/symlink/ua7805.pdf.
Zalman FanMate II fan controller use exactly this design, except that they skipped both caps. Given the small heat sink they use on the 7805, that product can only handle 0.5A at 12V (i.e. 6W), where a typical 7805 can handle 1A with a proper heat sink.
Worth noting that this use of a linear regulator is fairly ineffective and wasteful, a lot of energy will be converted to heat and radiated away. Still, it is a very simple design.