C/DART is a database recovery tool for analyzing and repairing C/SIDE databases.
Basically you used C/DART to open a Navision database. C/DART does not check if the data base is corrupt or not, and lets you connect no matter what.
You were then able to roll back till you find a version you want. The tool then allowed you to save the database rolled back at a non corrupt version. I have used it for many different fixes, the most common two are 1/ A corrupt sector or some other disk corruption, where you can then roll back to a valid version, and be back running again, and 2/ recovering a deleted database. You can completely delete all companies in the database, and then just click the undo button to get them back.
C/DART's only problem, is that Navision would never let it out of their offices, the reason being, that the program is so simple, it would be simple to debug, and thus work out how the database works.
C/PLEX is even more interesting. It was released in Navision Financials 1.10 or 1.30 (which?).
It was only released in a few countries, but the option has always been on the table properties, in the online help, AND for a short time on the price list.
C/PLEX basically allowed you to store a table on a server other than C/SIDE, eg. SQL or Oracle. This is nothing like the Navision SQL option. Think of C/PLEX as being the complement/opposite of C/FRONT. It allows Navision to access data in an external database.
(Captured from: http://dynamicsuser.net/nav/f/106/t/9883)