Komodo 5 (single processor version) is now available too, there's a download link on the komodo homepage:
http://komodochess.com/

To answer ghenghisclown's question, on one core it's rated 3122, compared to, say Deep Fritz 13 on 4 cores, which is rated 3050. Rating lists don't tell the full story, Komodo excels as an analysis engine, the rating lists are all at time controls much shorter than serious analysis.

Available for download at http://komodochess.com

Komodo 3 was previously the last free version, and Komodo 4 was the first commercial release of this chess engine that is a collaboration of Don Dailey and GM Larry Kaufman. 

Komodo 4 is roughly 45-50 Elo weaker than the latest commercial release, Komodo 6, on a single processor and does not support multiple cores. However, it is still very strong and useful, and it works exceptionally in Aquarium's IDeA. 

This release follows the very sad news that was recently delivered by Larry Kaufman:

"Don Dailey, my partner in the Komodo venture, has been transferred to a palliative care unit in the hospital. His leukemia has progressed to the point of no return, and he probably has only days left to live. His wife Mary agreed that it was better to inform the community of this rather than to wait until he dies to say anything. Don is at least glad to hear that Komodo will probably be in the TCEC final; hopefully he will at least live long enough to see that become definite. Don is 57 years old; a full obituary will appear here at the appropriate time.

Komodo will continue as a partnership between me and Mark Lefler, with Mary Dailey receiving an equal share of the proceeds. I'm in the hospital myself now, but I should be going home tomorrow with no further trouble expected. "

And indeed that latest development version of Komodo has reached the TCEC Superfinal with Stockfish, ahead of Houdini.