Half a decade after its release, the Galaxy S is still a capable handset, fact proven by the unofficial Android 5.1 build for it that has just been published on the XDA Forum.
http://www.notebookcheck.net/Samsung-Galaxy-S-gets-unofficial-Android-5-1-firmware.138175.0.html
Glad to see not everyone gave up on the SGS1 yet! I'm running Cyanogenmod 11 (Android 4.4.4) on mine and was disappointed to see that there isn't (and most likely won't be) an official CM12 build for it. Though it's also understandable: single-core Cortex A8, 512 MB RAM and pretty slow (by modern standards) storage are imposing serious limitations - most modern low-budget phones are nowhere near as laggy unless they're burdened with manufacturer "improvements". No point developing a ROM for a phone that can't even run it smoothly other than as a proof of concept.
Firefox OS would be interesting to see running on such older devices. My ZTE Open C feels quite snappy with it, too bad I got it with 1.3 and didn't get an update to 1.4. :(