Originally developed as a pre-surgery anti-microbial scrub, PHMB was patented in 1977, and marketed for pools and spas under the trade name Baquacil. This technology has the distinction and the EPA approval as the only non-halogen sanitizer available for pools and spas. Here's a page if you're looking here to find out how to convert back to chlorine or some other sanitizer.
Now that the patent has expired, Bio Lab has also introduced a line of biguanide products under the name Soft Swim. A full system for complete halogen free water care, these products are a stand alone alternative to traditional sanitation methods. The Biguanide itself is combined with algaecides and hydrogen peroxide for periodic oxidation. The system tends to gum up filters, and of course a product is available to de-gum it. Biguanide are not recommended for spas or aerated pools. As long as you don't add any other chemicals but those recommended by the manufacturer, you'll do fine; but add a small amount of chlorine and your pool looks like orange sherbet! Biguanides are also incompatible with TSP, ozone, detergents, ionizers, and other common chemicals, but is not at odds with any water balancing chemicals you may add.