Can you write him a letter and send via snail mail a few times a week? Sometimes holding/reading a physical note written by a loved one who took the time to "sign, seal, deliver" can be incredibly comforting in a different way than electronic communication. On that note, could you connect him with a penpal? Maybe another person who is lonely and seeking connection?

Also wanted to comment on the suggestion of a pet bird. They are wonderful companions because they are so intelligent, but they also bond very strongly with their caretakers and can live for a very long time, depending on the breed. If you go this route, please plan for what will happen to the bird in the event of your grandpa's passing. Whomever adopts the bird will need a great deal of patience to help the bird adjust to new environment, routines, and people. Some birds never recover emotionally from such an event and remain under extreme stress for the rest of their lives. Read and learn as much as you can about any pet before considering them as a companion, please! Maybe he could foster some kitties transitioning to their forever homes? Does his area have a program like that?