Are there sites for posting unpaid vacancies?

Question

open source

Currently, there are a fairly large number of non-commercial open-source projects, many of which lack people who have the free time, desire and skills necessary to develop this or that aspect.
At the same time, there are certainly people who would not mind participating in a free project "just for fun" at their leisure, for general development, experience and reputation (AFAIK authorship and co-authorship in interesting free projects is an advantage when applying for a job), but they don’t know what project and what part of it to take on.
So, are there any sites (besides the projects’ own bug trackers) where free projects that need human resources to solve certain problems could write, say, “a front-end developer is required” (let’s say the team has an interesting idea, but the team consists exclusively of server-siders, who have neither the skills nor the interest to develop a beautiful and user-friendly UI) and be heard by front-end enthusiasts?

Answer 1

Many job boards have a “volunteer” section, and they post there. But this does not apply to your task of writing a frontend))) Write on thematic forums.

Answer 2

In my opinion, some job sites have such a section (internship, volunteering) - career.ru , friendwork.ru . But usually they are watched by people with little experience, which is logical. You can try to go to events where startups and people who want to work there go - FriendWork FEST , hackday.ru, etc.
True, the chance is low, to be honest. It's easier to look for offline hangouts for opensource developers and related forums.