Without a doubt it has to be the internal company search engine/file finding tool @thewamz and I wrote.

The company has a wide UNC network with files scattered all over the place and they need a way to keep track of where the files get moved to (they can and do get moved). The original tool was written in Java/Tomcat and didn't use any frameworks or utilities beyond custom written ones, no orms, and the SQL was just raw strings. The program didn't take into account that files might be moved or deleted so it never removed anything from the database, it just kept adding files and never removing them.

It however never stores files itself, just links to files elsewhere on the UNC network.

It took six months to get it into what might be a stable beta or release candidate state. The user interface is good, very simple and intuitive, the whole thing was rewritten in python/django, there were issues with utf 8 (and mysql not fully supporting utf 8 in its own utf 8 mode), we added a regex search mode (which was sorely lacking), the search used to take up to fifteen minutes however we sped it up to less than a minute (worst case when a user simply puts "^$" as the regex search). It has a multi threaded design which does some checks to ensure it doesn't spawn too many threads and get stuck in constant Gil switching. Still some bugs to fix, like moving the processing of results returned by the server in a web worker so that the content widget doesn't lock up processing millions of search results and moving the back end to use asynchronous python might gain a performance boost. But on the whole I think the system is ready to replace the older system that all the users are frustrated with and constantly complain about.

However the annoying bit is... How to actually get the new system online, while I am responsible for the development of tools and their maintenance, I am not responsible for their initial deployment and that means I have no idea when (or even if) my new tool will even ever be released :/