We won't open source, for a variety of reasons. One reason is that if we serendipitously meet the right dev/hiring manager, we will hire them and revive the project. Secondly, as all bigcos who randomly outsourced a dead project can tell you, OSSing a huge project solves no real problems. Thirdly, neither of us will run an OSS project for it, and fourthly, it's a bit of a beast. You can't just pop Charm on heroku and expect it to run at speed. So, no OSSing.

As for the architecture, it was a Rails app with fully-live Backbone/CoffeeScript UI, a tuned Ruby cron job for scraping mail (POP, IMAP), a Postgres database and I forget which full-text search engine because we must have tried all of them before we settled on one. Nothing terribly fancy.