Tom Preston-Werner, co-founder of GitHub, is in Moscow for the Mail.ru Tech Forum and is hosting an informal gathering called a GitHub Drinkup at Sally O'Brien's. The event starts at 21:00, where attendees can meet him and enjoy the first round of drinks provided by the host. Preston-Werner can be identified by his distinctive gray GitHub shirt with "fork you" emblazoned on the front, inviting a casual and friendly atmosphere for those interested in networking and discussing technology.