I've built a flight planning tool for complex itineraries https://flightnotebook.com/ (bad timing, I know)
Historical job vacancy tracking website https://careerspulse.com/
And topping it off with releasing a full-text search query builder for Postgres + Rails to github (https://github.com/wyozi/pg-searchable)
If comprehensive, the back-end employment data may be valuable to DIY quants. Consider selling it on Quandl or the like.