user13744: Are there some free chess game databases where it is possible and allowed to download games? Is it possible to use this information for my own purposes? For example, would be allowed to make a machine learning app that learned from the downloaded games?

user29549: Mere aggregation is not protected by copyright in the US. Copyright only protects creative production, not a collection of facts as stated above. Annotations and comments might be copyrighted but it wouldn't add any copyright collection to the moves in the game.

user24916: I would add the Lichess Elite Database to the list :-)
It is the best of lichess games: only higher-rated players in "decent" time controls (aka no bullet).

user4418: Caïssabase is one of the biggest and best.
From the website:

What is Caïssabase?
When I got back into Chess a year or two back I couldn't find a decent
free regularly updated database of Chess games.
There are some good ones out there like Kingbase and Millionbase (not
updated anymore).
...
What is in Caïssabase?
CURRENTLY 4.02 MILLION GAMES
I started from the following databases/sources.
Millionbase
Kingbase
I then merged in all of the TWIC back issues up to the date on the archive as well as all the master games from pgnmentor.
...
What about curation?    Glad you asked. Roughly I followed these rules.

Removed all duplicates
Removed all games with less than 5 moves
Aimed for all games to have one (or both) players at least master strength
Fixed names and event spellings where possible
Inserted ELO's where known
Inserted extended ECO opening codes



...
Legal/Copyright
Where I live facts are not copyrightable, Chess moves played in a game are facts.
You'll notice there are no comments on any of the games as comments are copyrightable.

The latest download is from September 2019, so perhaps the intention of a monthly download is proving a bit too much. Meanwhile I've downloaded it for use with Scid vs PC and will be a grateful user.
Edit: There is a new download available as of 14th November 2020 with a new goal of updating once a quarter.

user-1: I would like to add a caveat against the blithe assumptions that chess games/score are not possible to copyright.
Individually, probably not.  But as a collection, 'catalogue copyright' just might apply.
In some places, catalogue copyright is used for works that normally could not be protected by copyright, but which still merit some form of protection. Lists, catalogues and directories are typical examples: the protection time is usually less than 10 years.
If it does apply or not depends on the situation: is it national law (say, US Copyright law) that applies?  is it the Berne Convention?  The World Copyright Convention?  Or even individual trade agreements between two countries?
It would almost certainly not be applied for fairly small, random downloads: it might however be applied for full download/dump of a chess database. An organization that plans to use it may add identifiable material that makes it possible to say where the information was taken from.

user825: 
FICS database

Lichess database

Million base 2.2

PGNMentor

Is it possible to use this information for my own purposes



Absolutely! Nobody has the copyright. Enjoy your machine learning adventure!

13744: <p>Are there some free chess game databases where it is possible and allowed to download games? Is it possible to use this information for my own purposes? For example, would be allowed to make a machine learning app that learned from the downloaded games?</p>
 29549: <p>Mere aggregation is not protected by copyright in the US. Copyright only protects creative production, not a collection of facts as stated above. Annotations and comments might be copyrighted but it wouldn't add any copyright collection to the moves in the game.</p>
 24916: <p>I would add the <a href="https://database.nikonoel.fr" rel="nofollow noreferrer">Lichess Elite Database</a> to the list :-)
It is the best of lichess games: only higher-rated players in &quot;decent&quot; time controls (aka no bullet).</p>
 4418: <p><a href="http://caissabase.co.uk/" rel="nofollow noreferrer">Caïssabase</a> is one of the biggest and best.</p>
<p>From the website:</p>
<blockquote>
<p><strong>What is Caïssabase?</strong></p>
<p>When I got back into Chess a year or two back I couldn't find a decent
free regularly updated database of Chess games.</p>
<p>There are some good ones out there like Kingbase and Millionbase (not
updated anymore).<br />
...<br />
<strong>What is in Caïssabase?</strong><br />
<strong>CURRENTLY 4.02 MILLION GAMES</strong></p>
<p>I started from the following databases/sources.</p>
<p>Millionbase<br />
Kingbase<br />
I then merged in all of the TWIC back issues up to the date on the archive as well as all the master games from pgnmentor.<br />
...<br />
<strong>What about curation?</strong>    Glad you asked. Roughly I followed these rules.</p>
<ul>
<li>Removed all duplicates</li>
<li>Removed all games with less than 5 moves</li>
<li>Aimed for all games to have one (or both) players at least master strength</li>
<li>Fixed names and event spellings where possible</li>
<li>Inserted ELO's where known</li>
<li>Inserted extended ECO opening codes</li>
</ul>
</blockquote>
<blockquote>
<p>...<br />
<strong>Legal/Copyright</strong><br />
Where I live facts are not copyrightable, Chess moves played in a game are facts.</p>
<p>You'll notice there are no comments on any of the games as comments are copyrightable.</p>
</blockquote>
<p>The latest download is from September 2019, so perhaps the intention of a monthly download is proving a bit too much. Meanwhile I've downloaded it for use with <a href="http://scidvspc.sourceforge.net/" rel="nofollow noreferrer">Scid vs PC</a> and will be a grateful user.</p>
<p>Edit: There is a new download available as of 14th November 2020 with a <a href="https://twitter.com/caissabase/status/1327686420274802691" rel="nofollow noreferrer">new goal</a> of updating once a quarter.</p>
 -1: <p>I would like to add a caveat against the blithe assumptions that chess games/score are not possible to copyright.</p>
<p>Individually, probably not.  But as a collection, 'catalogue copyright' just might apply.</p>
<p>In some places, catalogue copyright is used for works that normally could not be protected by copyright, but which still merit some form of protection. Lists, catalogues and directories are typical examples: the protection time is usually less than 10 years.</p>
<p>If it does apply or not depends on the situation: is it national law (say, US Copyright law) that applies?  is it the Berne Convention?  The World Copyright Convention?  Or even individual trade agreements between two countries?</p>
<p>It would almost certainly not be applied for fairly small, random downloads: it might however be applied for full download/dump of a chess database. An organization that plans to use it may add identifiable material that makes it possible to say where the information was taken from.</p>
 825: <ul>
<li><p><a href="http://ficsgames.org/" rel="nofollow noreferrer">FICS database</a></p>
</li>
<li><p><a href="https://database.lichess.org/" rel="nofollow noreferrer">Lichess database</a></p>
</li>
<li><p><a href="https://web.archive.org/web/20190124214300/http://www.top-5000.nl/pgn.htm" rel="nofollow noreferrer">Million base 2.2</a></p>
</li>
<li><p><a href="https://www.pgnmentor.com/files.html" rel="nofollow noreferrer">PGNMentor</a></p>
<blockquote>
<p>Is it possible to use this information for my own purposes</p>
</blockquote>
</li>
</ul>
<p>Absolutely! Nobody has the copyright. Enjoy your machine learning adventure!</p>
