Android 4.4 KitKat might tout its ability to run great on hardware with as low as 512MB of RAM, but that doesn't mean manufacturers are going to be updating older devices to the new version of Android. The Galaxy Nexus isn't getting an official update, so the Nexus S never stood a chance either, but thanks to the development community, Nexus S owners can now taste the sweet flavor of KitKat.
Developed by XDA member cn.fyodor, the ROM is said to work pretty fast, so it looks like Android 4.4 does improve things for old/weak hardware. It's an alpha build for now so there are a few issues such as some Google apps not working properly, but you'll be able to make calls, browse the web, and do pretty much everything else, even though the ROM might not be daily driver material yet.
Hit the source link to head to the official ROM thread on XDA and give Android 4.4 a go on your aging Nexus S and breathe new life into it. As always, take backups, and be careful while attempting anything.