SCP Tracker
A browser extension for Chrome and Firefox that remembers which SCP wiki articles and tales you've read. I built it because I kept losing track of which skips I'd read.
Chrome Web Store / Firefox Add-on / Source
Scroll to the bottom of an article and it gets marked as read, or you can mark things yourself from the popup. It also shows what you have and haven't read, gives definitions when you hover over SCP terms, links SCPs that reference each other, and has an optional reader mode.
It works on the main wiki, the Wanderers' Library, and most of the international branches. You can export and import your history. Reading history and settings use browser storage, including optional browser sync; the extension has no server of its own.
Outcome
It's on both the Chrome Web Store and Firefox Add-ons, and around 150 people use it daily.
The published version's source repository is archived. University has left me less time to work on it, but I am working on an update.