Gwet (2014) introduced a generalized version of Scott's pi coefficient, which is equivalent to Fleiss' kappa when applied with nominal weights. I recommend you read more about it in Gwet (2014). I'm also providing the formula here:
$$\pi=\frac{p_o-p_c}{1-p_c}$$
$$p_o=\frac{1}{n'}\sum_{i=1}^n\sum_{k=1}^q\frac{r_{ik}(r_{ik}^\star-1)}{r_i(r_i-1)}$$
$$r_{ik}^\star=\sum_{l=1}^qw_{kl}r_{il}$$
$$p_c= \sum_{k,l}^qw_{kl}\pi_k\pi_l$$
$$\pi_k=\frac{1}{n}\sum_{i=1}^n\frac{r_{ik}}{r_i}$$
$\pi$ is the chance-adjusted reliability index
$n'$ is the number of items that were assigned to any category by two or more raters
$n$ is the total number of items
$q$ is the total number of categories
$r_{ik}$ is the number of raters that assigned item $i$ to category $k$
$r_i$ is the number of raters that assigned item $i$ to any category
$w_{kl}$ is the weight associated with two raters assigning an item to categories $k$ and $l$ respectively
There are different weighting schemes available. More information on weighting schemes is available here, and more information on the generalized pi coefficient is available here.
References:
Gwet, K. L. (2014). Handbook of inter-rater reliability: The definitive guide to measuring the extent of agreement among raters (4th ed.). Gaithersburg, MD: Advanced Analytics.