While the SailfishOS UI (Silica/Lipstick) and Maemo 5's Hildon desktop are very different, I think SailfishOS is the closest you can get to Maemo 5 at the moment. There's a package manager, a terminal with full access to / and no limitation like Harmattan had, an official repository, and each developers on Openrepos have their own repository that you can add either manually from CLI or using an application. Multitasking is also similar to Maemo 5's. You can see it in action in the video I posted in a previous message here.