Minicom on Linux works excellently.

TextView 1.1 from 1993 is a text file reader that will work both with all 3/3a's and Pocket Books. As of October 2020, you can download it from http://www.sprightly.co.uk/psion3/series3.html.

If you have a 3a/Pocket Book II you might like to try a different program called eTxtReader which (I think) has more features.

Extract the 'Textview.app' file from the zip file.

Plug the 3-Link/A-Link into the side of your Psion and connect up the other end to your PC - probably via a USB-to-serial connector.

Press Menu -> Apps -> Install Application and install 'Comms.app' from the C-drive (which is actually your 3-Link/A-Link). This adds 'Comms' to the Psion's main menu. Open it up - you should be faced with a blank screen.

You need to set the transfer protocol to Y-Modem. To do this, press Menu -> Transfers -> Protocol and scroll right until you see YModem. Press ENTER.

On your PC, open up your terminal emulator program and set it to transfer the file 'Textview.app' to your Psion via the Y-Modem protocol at 9600 baud. Start the transfer on your PC first.

Now, press Menu on the Psion (whilst still in the Comms program) and go to Transfers -> Receive. Enter 'APP' where it says 'To name' and hit ENTER. The TextView program should now transfer over to your Psion.

Go to the main menu and press Menu. Choose Apps -> 'Install application' and select 'Textview.app' which will be on your Internal drive.

The fun bit - finally! You might like to try Project Gutenberg (http://gutenberg.org) - a library of out-of-copyright books that can be downloaded freely and legally in various formats. Make sure you choose plain text.

What constitutes a 'manageable chunk' depends on how much memory your Psion has. I have an Acorn Pocket Book I (i.e. an original Psion Series 3) with 256K RAM and I find 100-120K is about as much as it can manage in one go.

Make sure each chunk has a short file name (e.g. book1.txt) as otherwise things can go wrong when you transfer them to the Psion.

Start the transfer on your PC first, again using the Y-Modem protocol. Open up the Comms app again on the Psion. All the settings should still be set from before, so you just need to go Menu -> Transfer -> Receive. This time enter 'TXT' where it asks 'To Name'.

When you go back to the Psion main menu (and update the desktop lists, if necessary) the TextView app icon should be visible, with the name of your book underneath. Hit ENTER over the name of your book and it should open. Enjoy!

I'll write a bit more about how to deal with issues with the TextView app soon.