Stacksity - I think the concept of this is pretty great - it's really simple looking but it's obviously well put together. Subreddits here are 'stacks' and while these stacks aren't moderated the better content does rise to the top and you can explore various areas fairly easily once you have an account and subscribe to those that you're into.
I must admit I do find the $ prefixing everything kinda obnoxious though.
However nothing gets removed as far as I can tell and it's new so we should really cut it some slack and see how it grows. I'm looking forward to seeing how it expands.
Voat - Voat is essentially a Reddit clone - and that's OK. They have a karma system and the community is nice and welcoming and very open to discussion. It's very basic looking and if you're familiar with how Reddit works you'll be familiar with Voat works.
They get a lot of flak for being down often but it's run by a small but dedicated team who take donations to try and keep the servers up so it's rather admirable that they're doing as well as they are as whenever Reddit messes up people throw it around to immediately jump ship.
It's fun and fairly light though.
Snapzu - Snapzu is a much more polished looking link aggregator. You can post 'snaps' which are links/content to various channels that they call 'tribes' and it has a wide variety of subjects for you to explore. There's a rep system which accumulates over time with titles for you to get - but it does mean that those who have signed up earlier get more perceived clout than those that are new. At the moment you have to request an invite to join BUT they tend to dish those out quickly enough.
I have to say though it's not as...strongly opinionated as Reddit which is a good and a bad thing as it lends to very passive and dull comments.
Campus Society - This is purely aimed at university and college students so this won't be of any appeal those who aren't attending. You're grouped into channels where you can instant chat / post content with other students in your classes and university. This went live on Monday so it's very new in beta but there's also groups you can join similar to subreddits where you can chat / post and it's proving popular in London for a way of meeting new people who are at your university but haven't met yet.
It doesn't rely on upvotes / likes to determine user score but a 'GPA' system which goes up if users respond well to you and down if you're inactive over a long period of time or get reported by other users.
Full disclosure I'm part of the team here but if you have any questions I'm happy to answer them! (If your university isn't featured let me know and I can check that out)
Wechat - Now most people assume that this app, and sorry it's app based, is primarily just for the Chinese due to it's massive Chinese audience. Which is fair as it used to be Weixin and it did start in China. It does however have a massive, and very engaged, English speaking community and while there's as bit of culture clash it's actually a very interesting community to be a part of. However to find good content you have to find public accounts from people who post that content so you do end up having to put a bit of work in to find content you like.
I really enjoy the personal touch of that because there's a much more personal connection with these people as they tend to respond often, use actual names/faces, and have a real passion for what they're doing but it can be rather intense at times.
Aether - Another app based community however it's on the otherside of the coin. While Wechat is a hyperactive platform where you use your real name etc this is much more private scene which uses anonymous posting.
They're not likely to go down anytime soon though because their infrastructure does not rely on a centralised server setup but p2p. Their goal originally was simply to be a purely anonymous reddit so if you're privacy orientated this might be interesting for you but as it's links and not images etc most people might not find it that interesting - especially as it's in dire need of content and as anyone can pretend to be you it's hard to build any sense of community.
Yik Yak an interesting concept but the execution leaves something to be desired for the most part. Recent changes have improved the flow of conversation though which is good as you can identify who you're responding to and the community has taken steps to help cut down on abuse which was a problem early on. Yaks with -5 are deleted so the community polices itself.
Yaks are text based though and very short form so this might not appeal to everyone but it can be rather lighthearted and interesting for localised content.
The Student Room - This is an old school forum really primarily focused on UK students but it's got a wonderfully dedicated moderation team and a strong core community who are extremely helpful. Like most forums it is broken down into a wide variety of subjects/interests and users build rep through going their posts liked etc.
It's rather solid but it is definitely focused more on the UK student crowd.
Stumble Upon - This is how I found Reddit originally about 4 years or so ago as Digg was blocked at work. Stumble Upon is rather simple in its approach but it's a great way to view all types of content. Simply signup, select your interests, then click the Stumble Upon button and it'll randomly select you a tagged page/article/video based on what you selected. The community isn't really that big on commenting and what not, per se, but there is certainly something very addictive about clicking that button for new content.
Honestly I had so much love for this website I fear to go back.
Hacker News - This one is more for the tech orientated crowd and despite the overly abused 'hacker' title it's a great site for keeping in the loop with changes in the tech industry and for new and upcoming sites and startups.
After /r/technology took a tumble in quality I ended up just going back to Hacker News for quite awhile to be honest as it's simple, practical, and the community is very informed and helpful.
Product Hunt - This is a dedicated community focused on sharing and talking about the latest websites and startups. It's invite only if you want to discuss but you can vote until PH decide you're worthy of commenting. Some people complain of them being a tad elitist but I've met the team first hand and they're pretty dedicated to focusing purely on making a platform that's about showcasing the latest and greatest.
Though it does get a bit dull seeing the same people leaving comments and the discussion can be pretty thin.
Tumblr I'm expecting a bit (see lot) of flak for suggesting Tumblr but if you stay away from the echochamber angry ranty people and explore some of the more popular tags you'll find that there's a whole wealth of quality content worth reading. They're more into their TV/Film fandoms and so if you're not able to stomach that kind of thing you might want to pass but for lighthearted content it's not that bad.
Personally it's not to my liking but it's a viable alternative that while hated on will more than likely have something to cater to your taste.
Newsvine - I really like Newsvine - it's a small company that focus on linking out news but it's nowhere as extreme as /r/worldnews and the community is rather interested in current events. Discussion is small / limited however so you really have to put some effort in to generate discussion but it can certainly be worth it if quality and not quantity of replies work for you.
Frizbee I really dig how Frizbee are with anonymity and their general mission. Their mods are vocal but friendly but best of all their against censorship and really want to see their community grow in line with that. Which pretty much lends well to open discussion. They're in beta and while the site could do with some fine tuning it's a great experience despite the lack of polish.
What is interesting (see annoying as it happened to me) is that users can take your account if you don't fully register it. So uh yeah if you want that account name damn well do the sign up process.
It can be a little messy though as the default page throws everything into "Any" as opposed to a space, which function like subreddits, but I kinda do like that as it reminds me of how /r/all used to be.
Seriously though props to this guy if it's just the one person as it's really well done.
Other sites, but I'm not familiar with them and will update post once I know more: