A number of software products these days are DualLicensed.

Perhaps a pioneer in this regard was Perl, which is distributed under the terms of the ArtisticLicense? as well as the GPL, but it is not the canonical example and not what people generally refer to as DualLicensed.

The canonical example would be MySQL. These products are written by commercial entities and provided under GPL for private use, but also sold for commercial use under a commercial license. (DansGuardian used to employ such a method, but now is only licensed under the GPL. It is sold for commercial use from the author's website, but that doesn't prevent you from acquiring it from another source.)

To a layman, the legal implications may be confusing. In such a constellation, once downloaded under the GPL, any redistribution of the product to anyone (including businesses) must be under the GPL. However, if you obtained your copy under a commercial license, you are bound to the terms of that license and may not freely redistribute that copy.

Of course, the company may (and, obviously in all likelihood, will) refuse to directly support users of a GPL licensed copy.

Thus, the company and all customers get the best of both worlds: everyone can use the product and create derivative works, but there is also a commercial entity behind it which will offer contracted support, so business owners and PHBs can sleep better at night.