Not in the Yunohost app catalog, but powerful enough for FOSDEM: Pentabarf (archived Wiki)(Github)
Unrelated to that, another perhaps useful piece of software in a formal setting was mentioned in a recent thread, Signaturepdf.
A previous employer switched to a commercial service called docusign, which was even more hell to use than the previous procedure of attaching contract to mail, recipient printing it, scanning the result with signature, company receiving a picture-only contract back in the mail, which was then saved on a fileshare, but even so: it’s nice to see a Free Software alternative.