As per comment [1], here is a limited list:
```
|----------------+-------------------------------------------------+-------------+----------------|
| listing status | url | instance | # listed repos |
|----------------+-------------------------------------------------+-------------+----------------|
| done | https://0xacab.org/api/v4/projects/ | riseup | 883 |
| done | https://framagit.org/api/v4/projects/ | framagit | 12134 |
| done | https://gitlab.freedesktop.org/api/v4/projects/ | freedesktop | 1949 |
| done | https://gitlab.inria.fr/api/v4/projects/ | inria | 11112 |
| in-progress | https://salsa.debian.org/api/v4/projects/ | debian | |
| in-progress | https://gitlab.gnome.org/api/v4/projects/ | gnome | |
| in-progress | https://gite.lirmm.fr/api/v4/projects | gite.lirmm | |
| in-progress | https://gitlab.common-lisp.net/api/v4/projects | common-lisp | |
|----------------+-------------------------------------------------+-------------+----------------|
```
[1] https://forge.softwareheritage.org/T1111#20926