If only there was this simple utility, plugin, or small program that would make your life 10 times easier. I make those.
Terragen Render Manager: A great example of a custom app designed for a specific purpose: This was created for the internal use at Ixor 3D Ltd to manage the distributed rendering cycle of the program Terragen - a program that produces 3D landscapes. It monitors the rendering progress, collects and sorts the output, creates animated thumbnails of the rendered sequence, and orders the frame sequence as straightforward or interlaced. Rendering nodes can be added or removed dynamically from any running job. Display utilized a home-grown swing-based UI kit, too :)
Alumark: An MS-Windows program that let users create and preview quotes for custom aluminium sidings, as well as create order forms and reports based on those.
Groups: This Java app was created in 1997 for Windows, Linux, and Solaris. Groups was an IM program which featured custom backgrounds, a myriad of options, custom user icons, macros, message boards, file transfers, it could run from a PC or web page and much more, before Java, Linux, and the Internet became buzzwords. Some IM programs still don't have all the features this 10-year old program had. Pushed Java’s old AWT to it’s limits.
Ixor 3D's Online File Area: A small PHP/Java project created to enable large (as in 3D-rendering video) file distribution to and from clients for Ixor 3D Ltd
Buro: A plugin, interfacing with a popular stock trading platform's client, that allowed its user to rapidly execute specific stock trading orders, as well as make suggestions based on a custom high-frequency-trading algorithm.
SNMP bridging: When a client, under contract to a large Greek mobile phone operator, needed to interface their custom-built alarm system to the operator's SNMP monitoring, a lightweight Java app I made acted as the bridge between the two.