Ask HN: Looking for an open-source project to parallelise

I've just started a Parallel Programming unit at University and our major project (worth 50%) is to take an application and manually parallelise it to scale across multiple cores.

I'd like to do the assignment where the target:

* Is interesting

* Requires a fair amount of effort and skill

* Has some sort of barrier to making it parallel

* Is welcoming to me taking up the project

Does anyone know a project that fulfils most of these? The project's language or libraries aren't an issue.