P3.express is a non-proprietary, i.e. freely usable and distributable minimalist project management system. It is compatible with the leading standards PRINCE2, PMI PMBOK Guide and IPMA ICB, supported by the European Union and built so that you can start using it right away.
Its manual is freely available at https://p3.express/manual/v2/
It's only 45 pages long, so it's really minimalistic and easy to understand. It is freely available under the Creative Commons Attribution license. This means that you are free to use, share and modify it for commercial or non-commercial purposes, including, for example, creating your own project management methods or guidelines, training, etc. without asking for permission. Just mention the source and make it clear whether the content has been changed or not. According to the above license, it is not possible to revoke these freedoms (rights) in the future.
You can get certified according to P3.express. The certification is also minimalistic: it has only one level - Practitioner, comparable to, for example, PRINCE2 Practitioner, PMI PMP or IPMA C.
The certificate is valid for life, but it is recommended to renew it every year by retaking the exam according to the latest version of P3.express. Renewal of the certificate is free.
It is also possible to buy a course without an exam or an exam without a course.
Looking for an even smaller system for micro projects with 1-7 members? Then micro.P3.express - the "little brother" of P3.express is for you. Also free, released under the same Creative Commons license.