CodeEval has clunky UI/UX, not as comfortable as HackerRank and may confuse you with status of your submission. Apart from that it’s good enough to give it a shot. The community is not that big, something around 10k I guess.
CodeWars looks nice and feels nice. It’s focused more on sharpening language skills, so not too many languages are supported now, but you still have a lot of interesting problems to solve. Interesting ranking system and you can compare your solution with others.
SPOJ is also a well known place to practice your skills as well as participate and create in different contests. Haven’t used too much, but looks good. A lot of people recommend it.
CoderByte. Personally I haven’t used it, but it exists. At least this fact is worth of mentioning it :) Has not so many challenges.
The Project Euler only requires you to enter the right answer, therefore there is no restriction on the language you use. Incredibly popular as far as I know.
I'm starting a new open-source project "Open RSS Reader" that will be modular app so if you don't like the existing clients, you'll be able to quickly build your own. It's gonna be both open source and free to use.
`pet` is a simple command-line snippet manager. It allows you to write and store snippets for the command-line, so you don't need to remember all the commands you frequently use in you terminal. It can sync your snippets to the GitHub Gist, so you can always take your snippets with you.