Abandonware. It's impossible to buy it, despite it being available for download. It still runs fine on macOS 10.14 Mojave! But it won't run on 10.15 because the app is 32-bit.
For transition to a 64-bit disc cataloguing application:
1) EXPORT your DiskTracker catalogues to text.
2) IMPORT the resulting DiskTracker .dtc.txt file into your intended 64-bit disc cataloguing program.
3) VERIFY the resulting catalogue is accurate and properly formatted. If it's not, try importing it into another cataloguing program.
It's possible that a database program may more accurately import the .dtc.txt file, then let you export it again into a format that works for your intended 64-bit disc cataloguing program. OR a text editor may be able to reformat your database to be compatible with your intended disc cataloguing program. Be sure to use the correct extension used by the cataloguing program on the reformatted file before attempting to open it. If the reformatted catalogue is still not compatible with the intended cataloguing program, you'll quickly find out.
Thus far, my own experiments have NOT resulted in successful export/import into a new program. I'll keep trying. If others have succeeded, please post!