Perhaps SQLite would work for you. It's simple. It's crossplatform. And there's no need to learn a new language to build a frontend.
SQLite is implemented as an in-process library. There are bindings for all common languages, so you can almost certainly use your programming language of choice to work with it. Since it's a library of functions, there is no separate database process to connect to. The database itself is usually a local file, which you can fetch when needed or carry with you on a usb stick.
Your frontend could conceivably be as simple as using a sh script to wrap around the sqlite3 command line tool.
Or not.
Regards,
Alister