From the official website:
Give OUT Day is the ONLY national day of giving for the LGBTQ community – a 24-hour online fundraising event that unites the LGBTQ community from all 50 states, Puerto Rico, and D.C. to raise critically needed funds.
Throughout the day-long event, thousands of people make gifts to support a vast array of LGBTQ nonprofits across the country, ranging from the arts to social services agencies, advocacy groups to sports leagues, community centers to health care nonprofits.
Since its inception in 2013, over 23,000 individual donors have contributed more than $3 million and supported more than 500 different organizations in every part of the country. With changes and investments being made by Horizons, Give OUT Day’s potential is even greater.
Here's the link to a page with several national organizations you will probably know such as It Gets Better Project, National Center for Transgender Equality, PFLAG, Athlete Ally, and the Matthew Shepard Foundation.
Or you can search from the full list of charities taking part here.