user884: I often use the Pulsar engine to analyze my Atomic games for better play (post-mortem). I definitely learn something, since I am not as smart as Pulsar. I am interested in doing the same thing for Losers chess. Pulsar is not very good at Losers, but Sjeng is better at this variant.
I use both Pulsar and Sjeng under the WinBoard interface. Does anyone know of stronger engines that play Losers chess? I have Googled for several days, did not find any. Both Pulsar and Sjeng are free, but I would be willing to buy better software.
PLEASE NOTE
Many sites have confusing terminology for variants. Losers chess is not the same as Suicide or Giveaway. In Losers chess, the King can be checkmated, and you must respond to check. This makes a big difference in the strategy for Losers chess compared to Suicide chess.

user9926: The WinBoard Alien GUI is reputedly better suited to playing chess variants than the standard WinBoard is, but that's just an observation.
As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from get Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum ("Losers tournament" contains the pertinent tables, while the third & fourth pages of that thread contain two tables for their "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).
Sequenced in accordance with the engines' normalized mean averages of those tournaments:

Sjeng 11.2  . . . . . . . . . . . . . . . . . . . . . . . . . 0.885416(7)
Olithink 2.2.1 [OliPow] note A   . . . . . . . . . 0.5625(0)
Pulsar 2009-9b  . . . . . . . . . . . . . . . . . . . . . 0.411458(3)
Gerbil 02 note B  . . . . . . . . . . . . . . . . . . . . 0.3541(6)
KKF 2.6.6 . . . . . . . . . . . . . . . . . . . . . . . . . . 0.31708(3)
Nebiyu 1.41 notes C.x . . . . . . . . . . . . . . . . UNDEF. (0.275(+), est.)
PyChess note D  . . . . . . . . . . . . . . . . . . . . UNDEF.


Notes:

A: multiple other versions of OliThink 2.2.1 (in addition to those in the normalized list's link) can be had elsewhere (at the bottom, in the “Older versions:” section).
B: Gerbil ver.s 01 & 02 "...come with a separate executable for loser's chess...".
C: Nebiyu Alien has many additional [user defined] .ini files available as a collective package or individually.
C.1: Nebiyu can play Losers Chess, if you edit the winboard.ini (after which, “With -W (w17) [in the command line option] losers chess it works fine...”).
C.2: Note that Nebiyu might be “...playing atomic losers chess.” (later attested to the contrary by another).
D: PyChess wasn't one of the competitors, but can play Losers Chess, though it might be too weak an engine (in context of Losers Chess) to consider modifying for this purpose.


user1382: I've never used it myself, but I believe that Wizard is a strong and free Loser's Chess engine. An undated reference table on the same website shows that Wizard used to be one of the strongest Losers engines on FICS - however, I understand that the creator passed away many years ago so it may be outdated.

884: <p>I often use the Pulsar engine to analyze my Atomic games for better play (post-mortem). I definitely learn something, since I am not as smart as Pulsar. I am interested in doing the same thing for Losers chess. Pulsar is not very good at Losers, but Sjeng is better at this variant.</p>

<p>I use both Pulsar and Sjeng under the WinBoard interface. Does anyone know of stronger engines that play Losers chess? I have Googled for several days, did not find any. Both Pulsar and Sjeng are free, but I would be willing to buy better software.</p>

<p><strong>PLEASE NOTE</strong>
Many sites have confusing terminology for variants. Losers chess is not the same as Suicide or Giveaway. In Losers chess, the King can be checkmated, and you must respond to check. This makes a big difference in the strategy for Losers chess compared to Suicide chess.</p>
 9926: <p>The <b><a href="http://hgm.nubati.net/alien.html" rel="nofollow">WinBoard Alien GUI</a></b> is reputedly better suited to playing chess variants than the standard WinBoard is, but that's just an observation.<br></p>

<p>As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from get Pulsar.<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum ("<i><a href="http://immortalchess.net/forum/archive/index.php/t-12308.html" rel="nofollow">Losers tournament</a></i>" contains the pertinent tables, while the <a href="http://immortalchess.net/forum/archive/index.php/t-12308-p-2.html" rel="nofollow">third</a> &amp; <a href="http://immortalchess.net/forum/archive/index.php/t-12308-p-3.html" rel="nofollow">fourth</a> pages of that thread contain two tables for their "<i>Suicide chess tournament</i>" from which to infer Nebiyu's possible strength by comparison).</p>

<p>Sequenced in accordance with the engines' <i>normalized</i> mean averages of those tournaments:</p>

<ol>
<li><p><a href="https://sjeng.org/download.html" rel="nofollow">Sjeng 11.2</a> &nbsp;. . . . . . . . . . . . . . . . . . . . . . . . . 0.885416(7)</p></li>
<li><p><a href="http://kirr.homeunix.org/chess/engines/Norbert%27s%20collection/OliThink%20(Compilation)/" rel="nofollow">Olithink 2.2.1</a> [OliPow] <b><i>note A</i></b> &nbsp;&nbsp;. . . . . . . . . 0.5625(0)</p></li>
<li><p><a href="http://www.lanternchess.com/pulsar/" rel="nofollow">Pulsar 2009-9b</a> &nbsp;. . . . . . . . . . . . . . . . . . . . . 0.411458(3)</p></li>
<li><p><a href="http://web.archive.org/web/20070826142516/http://www.seanet.com/~brucemo/gerbil/gerbil.htm" rel="nofollow">Gerbil 02</a> <b><i>note B</i></b> &nbsp;. . . . . . . . . . . . . . . . . . . . 0.3541(6)</p></li>
<li><p><a href="http://kirr.homeunix.org/chess/engines/Jim%20Ablett/KKFCHESS/" rel="nofollow">KKF 2.6.6</a> . . . . . . . . . . . . . . . . . . . . . . . . . . 0.31708(3)</p></li>
<li><p><a href="https://sites.google.com/site/dshawul/" rel="nofollow">Nebiyu 1.41</a> <b><i>notes C.x</i></b> . . . . . . . . . . . . . . . . UNDEF. <i>(0.275(+), <b>est.</b>)</i></p></li>
<li><p><a href="https://github.com/pychess/pychess/wiki/StauntonRelease" rel="nofollow">PyChess</a> <b><i>note D</i></b> &nbsp;. . . . . . . . . . . . . . . . . . . . UNDEF.</p></li>
</ol>

<hr>

<p><b>Notes:</b></p>

<ul>
<li><p><b>A:</b> multiple other versions of OliThink 2.2.1 (in addition to those in the normalized list's link) can be had <a href="http://home.arcor.de/dreamlike/chess/index.html" rel="nofollow">elsewhere</a> (at the bottom, in the “Older versions:” section).</p></li>
<li><p><b>B:</b> Gerbil ver.s 01 &amp; 02 "...<i><a href="http://immortalchess.net/forum/archive/index.php/t-12308.html" rel="nofollow">come with a separate executable for loser's chess</a></i>...".</p></li>
<li><p><b>C:</b> Nebiyu Alien has many additional [user defined] .ini files available as a <a href="http://www.solidfiles.com/d/67f321a0a9/" rel="nofollow">collective package</a> or <a href="http://immortalchess.net/forum/showthread.php?t=12308" rel="nofollow">individually</a>.</p></li>
<li><p><b>C.1:</b> Nebiyu can play Losers Chess, if you <a href="http://immortalchess.net/forum/archive/index.php/t-12308.html" rel="nofollow">edit the winboard.ini</a> (after which, “<i>With -W (w17) </i>[in the command line option]<i> losers chess it works fine...</i>”).</p></li>
<li><p><b>C.2:</b> Note that Nebiyu might be “<i><a href="http://immortalchess.net/forum/archive/index.php/t-12308-p-3.html" rel="nofollow">...playing atomic losers chess.</a></i>” (later attested <i>to the contrary</i> by another).</p></li>
<li><p><b>D:</b> PyChess wasn't one of the competitors, but <a href="https://github.com/pychess/pychess/wiki/StauntonRelease" rel="nofollow">can</a> play Losers Chess, though it might be <a href="https://groups.google.com/forum/#!topic/pychess-people/1gq5Hsin4JI" rel="nofollow">too weak an engine</a> (in context of Losers Chess) to consider modifying for this purpose.</p></li>
</ul>
 1382: <p>I've never used it myself, but I believe that <a href="http://poincare.matf.bg.ac.rs/~andrew/suicide/StanGold/wizard3_1.htm" rel="nofollow">Wizard</a> is a strong and free Loser's Chess engine. An <a href="http://poincare.matf.bg.ac.rs/~andrew/suicide/StanGold/top20.htm" rel="nofollow">undated reference table</a> on the same website shows that Wizard used to be one of the strongest Losers engines on FICS - however, I understand that the creator passed away many years ago so it may be outdated.</p>
