The first application is ReKall. Rekall is TheKompany's answer to MS Access. Lots of people have asked for this kind of application for Linux, and TheKompany in response has issued this Preview Release version. The Upcoming KOffice will include a version of Rekall. Instead of using Visual Basic like Access does, Rekall uses Python, as well as plug-ins for MySQL, Postgre-SQL, and Informix (other plug-ins for the various databases will follow.) Note: Since Rekall is using KDE-DB (also a contribution to KDE by TheKompany) and KDE-DB will be available only with the upcoming KDE 2.2; you'll need to do some simple compilation and installation. All the instructions are available at their web pages.
The next product is Aethera -- a nice PIM manager to manage all your email as well as contact information. You might say it's competing with Evolution, but both of the projects takes different direction of implementation. Aethera is also expandable with Plug-ins. (Debian packages are also available).
While ReKall and Aethera are Open Source, the last one is a commercial product called Kapital, which is an Quicken/MS Money workalike. The product costs money (you can find those prices at the above link) and it has one of the nicest and easiest GUI's I've been played with. You can download the beta to test it and find for yourself. (Debian packages are available for Kapital as well.)