If you have a Nexus 5 you can experiment with, you can now experiment with Sailfish OS. A community port has been released, and while it's clearly not stable or anywhere near production-ready, it's still interesting to try out on your Nexus 5. It's not feature-complete, and several things don't yet work, but it's getting there.
The flashing instructions are pretty straightforward - in a nutshell, flash CyanogenMod, flash Sailfish on top of it, done. It's weekend, so have fun!