Q: First of all, what are they? (refurbished -post-)
A: They are all gaming platforms.
GarenaWAS the most popular DotA platform where players could play, from all around the world. Players from Europe, Asia, USA, can join their country rooms and have reduced lag and have people talking the same language, of their country. You can play other games like Counter-Strike (Source), Call of Duty, Borderlands, Age of Empires, Left 4 Dead and many other fun games ON Garena.
ICCup is another DotA platform, that is more advanced than Garena because it has a better ladder system and the chance to drop in-game is low. Beside DotA, you can also play SC, CS 1.6, Warcraft III-RTS-. I personally haven't played much on ICCup platform.
Ranked Gaming Client (RGC) is the newest DotA platform since 2010 and has a reliable gaming system with games hosted by bots. On the other hand it has an online ranked ladder where you can see your stats from all of your games. Ranked Gaming Client has bots from Europe, USA and Asia and some great league rooms like Anubia-ihl, Dota-League, EAL. Since i haven't played for a while, i don't know other leagues -i moved to DotA 2-.
Dotalicious-Gaming is an online-platform where you just have to download the Dotalicious-client and just click on the server to join a game. The most skillfully players i have seen where playing on Dotalicious-Gaming client. If you are bored of un-mannered or low skill players (noob=newbie) i recommend playing on Dotalicious platform.