I find group chats with different groups of friends and family has filled this niche. There's no ads. There's no technical barrier to entry. No need to even sign up for a service. The stakes are low, messages can just be a meme or some nice photos from a day trip. The only downside is the ephemeral nature of texting. Even then, my MIL figured out how to save pictures to her phone and they occasionally show up in the calendars she makes as Christmas gifts.