user23596: I want to organize a 6 round swiss tournament for 100+ players with 3 rounds/day.
I know there are websites which allow us to organize swiss tournaments
ex :- chess.com,lichess.org.
I want to know if there are websites which allow the swiss tournament to go on for many days.

user15365: Yes, Lichess Swiss tournaments allow a tournament to last several days.
But to achieve your goal of three rounds per day you will need to set the value of Interval between rounds to "Manually schedule each round". In that case, rounds will not start automatically like when you set the interval to "1 day(s)", for example.
Please notice that Lichess Swiss tournaments can only be created by team leaders, and can only be played by team members. The reason they give is that this type of tournament demand punctuality, dedication and patience from players, and these conditions are more likely to be met within a team than in global tournaments.
Also note that an odd number of rounds allows optimal color balance.

23596: <p>I want to organize a 6 round swiss tournament for 100+ players with 3 rounds/day.<br />
I know there are websites which allow us to organize swiss tournaments<br />
ex :- chess.com,lichess.org.<br />
I want to know if there are websites which allow the swiss tournament to go on for many days.</p>
 15365: <p>Yes, <a href="https://lichess.org/swiss" rel="nofollow noreferrer">Lichess Swiss tournaments</a> allow a tournament to last several days.
But to achieve your goal of three rounds per day you will need to set the value of <em>Interval between rounds</em> to &quot;Manually schedule each round&quot;. In that case, rounds will not start automatically like when you set the interval to &quot;1 day(s)&quot;, for example.</p>
<p>Please notice that Lichess Swiss tournaments can only be created by <a href="https://lichess.org/team/me" rel="nofollow noreferrer">team leaders</a>, and can only be played by team members. The reason they give is that this type of tournament demand punctuality, dedication and patience from players, and these conditions are more likely to be met within a team than in global tournaments.</p>
<p>Also note that an odd number of rounds allows optimal color balance.</p>
