Wanted: Membership software

Basics:
- For a non-profit client.
- They are willing to pay money.
- Preferably open source, based on open source

Requirements:
- Administrate international membership (Not just Anglosphere!)
- Process payments for membership
- Manage and organize Webinars/virtual events

Edit: Further Requirements:
- Profiles for Users with different roles e.g. different membership status

The client is currently looking at a proprietary solution that they are not entirely happy with and therefore are open to alternatives.