Since you don't mention your level of experience and/or what sorts of projects you have worked on and/or whether you have UI skills and in what framework, it's going to be difficult for people to decide how much effort they will need to expend.
As an earlier commenter hinted at, I would suggest trawling GitHub for any C/C++ projects that have tags matching one or more of your personal interests. Find projects that need support rather then just 'throwaway' projects and ask to get involved.
I have an idea for company and job candidate "virtual online dating" service. The interview process is broken. It is a hit and miss system. Many things can go against both the candidate and the company during an interview process; a good candidate may have a bad day on the day of the interview or the interviewer may have a bad day. A company's interview format may not be suitable for an excellent candidate, the interview process many have nothing to do with the actual work environment and projects the candidate will work on if hired etc. There are lot of issues with the present interview processes.
So the idea is to develop a platform where both candidates and companies can evaluate each other over a longer duration in the "online virtual work environment" setting rather than an artificially designed/borrowed few hours interview process. The project is basically a "show, don't just tell" approach to understanding both the candidate and the company over a period before either the candidate or the company approaches with a proposal to move to the next step.
Anyone interested in this idea? You will find my email on my HN profile page if you want to brainstorm this idea and work together.
Ok no worries. I might start an interesting C++ project soon. The idea is to build a deskop app that helps users to improve their privacy and security practices. I'm planning to use Qt (QML & C++) for the frontend and use "osquery" in the backend to get most of the required data. I'll put that on our Github (https://github.com/kiprotect) once I start, so if that interests you just ping me there!
As an earlier commenter hinted at, I would suggest trawling GitHub for any C/C++ projects that have tags matching one or more of your personal interests. Find projects that need support rather then just 'throwaway' projects and ask to get involved.
Just my 2c.