Once the FingerPrint service is running, iOS devices on the same network see the printers attached to your computer and can print to them through your computer, using its printer drivers. iOS's AirPrint service supports just basic printing options, such as number of copies and duplex printing, but FingerPrint supports even fewer. The duplex option, for example, doesn't appear, as it did for Printopia, Genie, the Lantronix xPrintServer appliances, and EFI's PrintMe Mobile.
FingerPrint also can "print" to JPEG or PDF files sent to your Mac or apps such as iPhoto, Dropbox, and Evernote.
Ecamm's OS X-only Printopia also installs as a service on Mac OX 10.5.8 Leopard or later, but you manage it through a system preference on the Mac. The company offers a time-limited trial version, so you can test it in your environment before buying.
Configuration options include paper size, color settings, toner efficiency, password protection for printers, the network port, and the printer icons in iOS's printer list to distinguish Printopia-enabled printers from other AirPrint printers). Like FingerPrint, it can "print" to JPEG or PDF files sent to your Mac or apps such as iPhoto and Evernote. Plus, you get the ability to select duplex printing for printers that offer that capability.
The simplest of the three application-based AirPrint options is the nicely designed Genie router-management app that comes with Netgear's WNDR and R series of wireless routers, as well as with its wireless repeaters. (I tested it with the WNDR3800, WNDR4500, and R6300 routers, all of which I really liked as routers.) You can download Genie from Netgear's website to as many Macs and Windows PCs as you have on your network -- there's no per-client price as with FingerPrint and Printopia.
There's a version for OS X 10.6 Snow Leopard or later, as well as for Windows XP Service Pack 3 or later. Note that the Genie iOS and Android clients let you manage your Netgear router but not AirPrint; you do that from the computer whose printers you are AirPrint-enabling. (It works only with selected -- meaning recent-model -- Netgear routers.)
On your computer, go to Genie's AirPrint pane and enable the printers you want to make AirPrint-compatible. That's it! As long as the computer and Genie app are running, its printers are available to iOS devices.