The Galaxy S II is an iconic device in Samsung's line-up. It had a big role in changing the public's perception of Samsung's brand and establishing it as a major smartphone player. But in our day and age, at a time when the S7 is about to be announced, the S II is getting long, really looooooooong in the tooth. It's a 5-year old device by now and its specs (dual-core 1.2GHz processor and 4.3" 480x800 display) can hardly be found in the lowest of the low-end Android phones. It does have 1GB of RAM and 16/32GB of storage though, which make it a potential candidate ripe for more modern Android ROMs.
Like CyanogenMod 13. That's Android 6.0, running on a device that launched with 2.3.4 and was only officially updated up to 4.1. If you've had an S II since day 1, you'd have seen Gingerbread, Ice Cream Sandwich, and Jelly Bean officially, then Kitkat, Lollipop, and Marshmallow through custom ROMs. That's a lot of candy.
Those of you who are still hanging onto their S IIs may have had a few other ported Marshmallow ROMs running on them, but this is the official CyanogenMod build we're talking about. It's a nightly so it won't be stable at first, and you'll need to flash this GApps zip package to get your Google apps working, but it's bound to be a cool weekend project at the very least. Provided your battery still lasts long enough to flash a ROM...