Winter of Code
Contrary to what the name suggests, these programs do not only take place in winter but at any time of the year other than summer. Unlike summer of code programs, these initiatives generally do not require a full-time commitment and do not include remuneration. However, prizes are often awarded to major contributors.
Hacktoberfest
Hacktoberfest is one of the most famous winter of code events. It is organized by DigitalOcean and has taken place every October for over 10 years.
Season of KDE
Organized annually since 2013 by KDE Student Programs, the program offers the opportunity to participate in projects (both programming and non-programming) for the benefit of the KDE ecosystem.
24 Pull Request
The idea of the initiative is simple: send 24 pull requests between December 1st and December 24th. The website suggests projects to contribute to.
Other Winter of Code
Many Asian organizations and universities organize winter of code programs. Below you can find some of them: