One top option is MobileGPT, which taps into OpenAI's GPT-3 and GPT-4 models for a broad range of abilities. It can handle conversational AI interactions, translate languages, solve math problems and even generate business documents. It also has more mundane abilities like note taking, reminders and job hunting.
Another top option is ChatGPT Buddy, a 24/7 virtual assistant built straight into WhatsApp. It uses GPT-4 to answer questions, generate text and images and translate text. It's designed to be easy to use and offers a variety of pricing plans for personal or professional use.
If you want something more customizable and adaptable, Botpress offers an end-to-end AI agent stack with integrations for WhatsApp, Telegram and other chat apps. It offers professional greetings, LLM integration, database synchronization and an API for customizations. Botpress offers a free tier with basic abilities and paid plans for more advanced abilities.