Sorry the angle is a little funky, but this is one of my two workhorses, the Casio BN-20. This guy gets used almost every day, and is my primary source of truth for my calendar and contacts. It was released in 1998 and has 2 MB of user memory. The spreadsheet function is pretty rudimentary, and the only function that I don't have a lot of experience with. The expense function is the best expense tool I've ever seen on an electronic organizer. I run Xubuntu on modern hardware and can sync the data using Casio PC Sync through Wine and with a USB to serial converter.
That is a well-filled pen! It looks like others have said this, but nothing has ever beaten my 90s PDA for organising my life.
Between the PDAs and my bullet journal, I'm pretty well set.