Chess engine with configurable strength?

It is as simple as that. I want an engine with a configurable strength that I can actually beat. It is not fun if you lose 100% of the time.

Arasan

A free engine which can adjusted at any elo rating.

For free there is Lucas Chess with dozens of low strength engines that give away pieces.  Commercially, all three of my programs can be configured at whatever strength you want: Fritz, HIARCS, and Chess King.  Hope that helps...

Arasan

A free engine which can be adjusted at any elo rating.

Fritz 5 is free

Stockfish is free.

It

There are over 260 engines on this list.  Most are free.  You should be able to beat most of the engines near the bottom of the list, especially if you give the engine just a few seconds to think, while allowing yourself as much time as necessary.

As ilgambittoo stated, Arasan is a good choice. Another good choice is Ufim 8.02; It's easy to install and can be set very low. A bit harder to install, but still a good choice is the Winboard engine Crafty 22.10. (You have to configure the Crafty.rc configuration file; maybe more work than you want to invest.)

Arasan:

http://www.arasanchess.org/

Ufim 8.02

http://wbec-ridderkerk.nl/html/details1/Ufim.html

Crafty 22.10:

http://kirr.homeunix.org/chess/engines/Jim%20Ablett/CRAFTY/ARCHIVE/older%20crafties%20%2820.0-23.3%29%20ja/

Shredder is best for this, I believe. You can download a free demo from their web-site

Yep, I agree with Matt. If you're willing to spend a little money, Shredder is nice. The link for the Shredder Classic 4 demo (30 days) is here:

http://www.shredderchess.com/chess-download/free-demo-download/download-shredder-classic-4-windows.html

(Shredder Classic 4 has an engine that's a little weaker than Shredder 12 at the strongest setting, but at the weak settings it's the same as Shredder 12.)

Of course I want free ones...

Stockfish is not configurable, is it?

Recent versions of Stockfish can be weakened. I think Ufim can be set even weaker than Stockfish, though.

If you have an iOS device, the "Play Magnus" app is worth a look. It uses an engine written by one of the main Stockfish authors that has been tuned to play like Carlsen at various ages from 5 to 23.

If it can be weakened down to about 1200 ELO (or if I want an easier match for fun 1000 ELO), then it is ideal.

How do you weaken stockfish? I can't figure out! I use a mac and Sigma Chess.

Assuming the Mac version works the same as the Windows version - Go into the engine configuration and change the skill level. Default is 20 (full strength) and weakest is 0. I'm guessing level 0 is maybe 1000 to 1200?

Thanks, I found it. But I upgraded to OS X Mavericks, and Sigma Chess stopped working. I then downloaded the Stockfish app, but turns out you can't play against it. Do you know any good chess GUI you can play with and install different engines?

No, I'm a Windows guy, but there may be a few people here who can talk about Mac stuff.

Hey, can you bring them 'round? 

Just joking. But I think I found a solution. I will play against the demo version of Shredder (Shredder normally costs money, quite a lot actually, but there is a free version for 30 days with a "low" ELO rating of 1600, and, since that is more than enough for me, I will uninstall it when the 30 days are over and then download it again, so that I can always have it. Don't tell anyone), and keep my nice little Stockfish (awesome mac app for analysis only) for my analysis and be happy. I would like to be able to play against Stockfish, but Sigma Chess does not work for OS X Mavericks. Sad. But Shredder will hopefully do the job.

I can install Stockfish in Shredder. Magnificient!