Although my day job keeps me in the worlds of web and mobile app development, I've spent over 20 years using Macs and have programmed them in a variety of languages.
Below are a couple of the projects I've written to share with others.
TNEF's Enough is a program I wrote to help Mac users deal with certain attachments from users of Microsoft Outlook and Exchange. The program is freeware so check it out if you ever receive weird attachments with the name "winmail.dat."
QR Journal is a desktop application to scan and store QR Codes. Scan with your Mac's iSight-compatible camera or drag and drop an image from emails/online. Decoded URLs from QR Codes can then be navigated to with your browser.