
Xojo makes an excellent choice of developing client/server database applications given the choices of Relational Database Management Systems listed above. Wth Xojo you can quickly build a front end user interface and you can easily modify it to accomodate new feature requests. Perhaps the best reason to use Xojo is because you can compile applications for Windows, Macintosh, and Linux while writing just one body of code.
Xojo Web Edition, a separate product from Xojo Software, allows us to develop a web interface to your data. See the Mobile Data section below for more details.

Most applications involve data of some sort hence the need for a database. If your application is going to be run locally on one machine at a time then the single user SQLite is fine and won't cost a dime. If your application is intended to be used in a multi-user environment then you will need a multi-user database system. Good choices are the free open source databases of MySQL, MariaDB and Postgres. Oracle and Microsoft SQL Server lie at the high end of the spectrum.