myBill is written in Java and uses internally hsqldb which is an open source RDBMS written also in Java and is included in the distribution zip-file. In other words there are no other requirements besides the Java VM. If by any chance you have not Java installed to your system, you can find it here
myBill needs no installation except downloading the latest zip file, uncompressing it and executing runApp.sh if you are on a unix-like OS (like Linux,*BSD,MacOS) or runApp.bat if you are using an MS windows flavor.You can download the zip file from here. Of course that means that you can use your copy from any kind of portable media like a usb stick or an external hard-drive.