JFlagCap will work on any machine that can run Java's JRE 1.6- which is most modern machines that run Solaris, Windows, or Linux. You can see the Java Download Page for information about Java versions and what will work on your machine.
jFlagCap has been tested on several computers and operating systems. It works reasonably well on older machines-- the oldest of which was a Pentium II 266MHz machine with 64MB of RAM running Debian Linux. It was playable with about a 1.5 second delay between turns with all the defaults. Since jFlagCap's turn-based, that is reasonable. jFlagCap was also tested on a 2.0GHz 64-bit Linux machine without a hitch with a < 250 ms. "tick". It was also run on the same 2.0GHz machine running 32-bit Windows 2000.
jFlagCap was developed in Linux and was designed for use with Windows rather specifically, as that is what most gamers tend to use. For testing purposes, I have burned the Windows installation to a CD and have been carrying it around for testing purposes. So far, it seems to perform solidly in Windows with or without having the JRE pre-installed. To use any command-line options, though, one must use the JAR (as the .exe files were clumsily written at the last minute). This will be fixed in a future version– which will come when there is a version ready to be released and not sooner.
The game and this website are both made by Mark Burger (currently seeking employment.) Feel free to contact either me or the jFlagCap forum if you have any questions or comments. If you prefer chat, I am on ICQ at 119420913.