Some people aleready know about the upcoming flash games based on the hit game, Super Smash Bros. Brawl. Well currently three of those have already come out with demos on their own sites. Here's what they are from my prespective:
Super Smash Flash 2
Author: Cleod-9 (McLeodGaming)
Original Smash game: Super Smash Flash
Sequel to the game on Newgrounds, it will feature more characters, an improved engine, more stages, and Final Smashes.
Details: Current demo features 8 characters; Mario, Kirby, Link, Sonic, Lloyd, Ichigo, Naruto, and Megaman. Their movesets are (seemingly) complete and they have operational Final Smashes. Mario, Ichigo, Naruto, Megaman and Sonic have transofmarion Final Smashes where their stats and movesets change slightly. Lloyd's and Link's Final Smash are contact Final Smashes. Kirby uses Cook Kirby. Currently there's 7 real stages (Battlefield, Hyrule Temple, Whispy Woods, Green Hill Zone, Mushroom Kingdom II, Waiting Room, and Final Destination) along with a random stage selecter. Several items from Super Smash Bros. Brawl also appear. On the Smash Flash Dojo (fan site), it mentions most of the planned items, characters, and stages. COM difficulty has improved since original version. Shields and Grabbing have been set. Random Character Select has also been added.
Last Updated: 11/20/09
Super Smash Duel (Discontinued)
Author: x2i
Original Smash game: Sonic Smash Brothers BETA
x2i's "slight clone" of Brawl.
Details: Current demos use an engine that, according to the author, was tossed in favor of a better one. The demos were released for the fans to use to get an idea of what the game might look like. Highly incomplete, as finishing a fight will freeze the game (thus requireing you to use Refresh). COM difficutly and Player's 3 and 4 have not been set. Most character movesets are complete (including Kirby), but are very different from Brawl. You would need to visit the official page for details on their movesets. Characters in version 1 are Mario, Luigi, Peach (no icon, but selectable when placed under Luigi), Sonic, Link, Kirby, and Pikachu. Verion 1.1 include Mario, Sonic, Jigglypuff (unfinished), and Pokemon Trainer with Squirtle (Nearly Complete), Ivysaur (Half complete) and Charizard (No where near complete). Stages include Battlefield, Yoshi's Island, Norfair, Pokémon Stadium, Bridge of Eldin, Warioware, Green Hill (v. 1), Mario Circuit (v. 1), Smashville (v. 1.1) and Frigate Orpheon (v. 1.1). Only one items exists in the v. 1.1 levels (Shadow Assist trophy, Pokeball with either Snorlax, Bellosom, or Electrode, and Heart Containers) and Smash Balls appear either at Random or when the End button on the keyboard is pressed. Final Smashes are similar to Brawl. I won't go into too much detail with this. In addition, x2i plans to custom make his sprites and has character drawings on the official site. The picture below is his own doing.
Last Updated: 7/10/08
Super Smash Bros. Brawl (temporary name)
Author: Runouw
Original Smash game: Super Slash Bros. Melee (renamed Brawl, unfinished, unavaiable on NG).
Out of anger and jealousy of Super Smash Flash 2, this guy decided to make his verion of Brawl. He currently has no name for it, using the original game's title screen for the time being.
Details: And enitre engine remake was made, so now there is no characters aside a blob called Gooey, no stages beside Battlefield, and no items beside an unbreakable capsule. Look out for an improvement.
Last Updated: 6/25/09

Super Nuke Bros. Melee.
Authors: Nuke Bros
Previous Smash Game: N/A
The Nuke Bros variation of the Super Smash Bros series in the works. Currently has 8 characters (Mario, Samus, Link, Pikachu, Sonic, Peach, Cloud, and Meowth) each with respective Nuke Smashes (The equivalent to final smashes) with only Mario's being 100% true to the original. Movesets seem to be still in the works, but are playable. There is also 14 total items available, a demo of the story mode, and the option to change your controls. There are currently five playable stages (Battlefield, Peach's Castle Grounds, Metal Harbour, Jungle Hijinx, and Tower of Guidance). Also, unlike SSF2 and Runouw's game, Nuke Bros. uses their own drawn characters as opposed to sprites.
Last Updated 11/20/09

So there you have an in-depth analasis of the three games. If you wish to try them out or find out more, visit their pages:
McLeodGaming Home Page
Super Smash Duel official homepage
Runouw's Sheezyart Profile
Super Nuke Bros. Melee Main Page

I will update this whenever I can. I would also like to know which of the three the people like best. Feel free to comment on that.
PS: I'm aware that there may be other clones out there. I won't write until I check out the demo of each game. I'll also take help on updates.Nuke Bros DeviantArt