New York State Homes and Community Renewal, known as HCR or DHCR, is the State's housing agency. It supervises rent regulation, Mitchell-Lama, and the money that finances affordable housing across the state. Two of the things it does show up directly in your neighborhood.
Neighborhood Preservation Companies are nonprofits DHCR contracts to provide housing services in a specific service area, sometimes called a catchment area. Most offer some combination of managing affordable housing, tenant rights counseling, help with repairs and code complaints, foreclosure and eviction prevention, help applying for affordable housing, and assistance for landlords of small buildings.
Services are generally free. Each company serves a (sort of) defined area. If you are reading this in CB6, the one closest to you is probably either the Fifth Avenue Committee or the Carroll Gardens Association.