The FHA
Despite its racist past, the Federal Housing Administration guarantees and administers one of the best mortgages for those establishing credit or with low funds to buy. Features: 3.5% downpayment, no minimum credit score, 6% Seller Help allowed. The FHA 203(K) renovation mortgage is tops for wealth building.
The VA
Eligible veterans have access to perhaps the most buyer-favorable mortgage on the market - the VA loan. Zero percent down, liberal credit underwriting, no limit on loan size (just the guaranty-higher down), and, yes, VA has a renovation loan.
Fannie-Freddie Conventional
Fannie Mae and Freddie Mac are Government-Sponsored Entities (GSEs) whose underwriting guidelines govern what most lenders will allow for non-government (FHA, VA, USDA, etc) or Conventional Mortgages. Credit requirements are higher as are downpayments, but wide varieties exist.
Investor-Commercial
Commercial loans for properties over 4 units residential or business properties are not regulated like 1-4 unit single-family home mortgages. Mortgage Loan Officers on 1-4 unit residential homes have to be licensed like Realtors. Investor mortgages are often based on the income the property will bring, especially 4 units+.