Much like Super Smash Flash 2, this one's for the PC. It's called Super Smash Bros. Crusade, and its massive roster of playable fighters include familiar faces like Mario, Bowser and Kirby, and lots of newcomers, like Ridley, Rayman, Crash Bandicoot, Klonoa, Krystal from Star Fox, and even Phoenix Wright.
Smash Bros. Crusade has been around since 2008, and it's still in active development today by a relatively large team of Smash Bros. fans. Its most recent update was just released last Sunday, in fact, after two years of development.
Apart from a 60-character roster, Crusade offers both offline and online play and a training mode, across 24 stages like Saffron City from Pokémon, the plane from Pilotwings, and Suzaku Castle from Street Fighter II.
Gameplay feels quite smooth, similarly to Smash Flash 2, though I found Ridley in particular a bit hard to control. Apart from that, the stages look good, the music's awesome, and the game even has its own announcer. So if you need to kill some time before Smash Bros. 3DS lands in a bit over a week, you might wanna check Crusade out. You can also look at the Project Crusade wiki to learn about the characters.
Super Smash Bros. Crusade Version 0.9 has been released [Indie DB] 0.9.0 Download Page [Smash Bros. Crusade Forums]