The Open Society Foundations usually fund within their own issues or areas of interest. They do not accept any Letter of Inquiry (LOI) openly from NGOs, but one can explore their vast number of grant opportunities available under different programs and then submit requests for grants in each of them. Many of these programs have regular call for applications or RFPs announced from time to time and some are open to proposals throughout the year.
As each of these programs have different forms of applications and/or LOI, it is best to go through them carefully and find out if they match your needs or not. Some programs provide grants only in some regions or countries of the world and some programs are focused on certain issues only. For example, the Human Rights and Governance Grants Program provides funding to NGOs only in Central and Eastern Europe and the former Soviet Union and Mongolia. To submit a Letter of Inquiry under this program, one has to submit a 2-3 pages concept note outlining the project description, about the organization and the estimated budget and timeframe of the project.
The Open Society Fellowship is one of the most popular programs of the Open Society Foundations. This fellowship is open to candidates from all countries and it is open once in a year. There is an application form available for this fellowship and only individuals can apply.
You can explore more about the various programs of Open Society Foundations at this link.
This donor agency also has its offices in various countries and regions that provide funding to NGOs locally.