FLAN-T5 is a finetuned version of Google's popular T5 model with instruct-finetuning. As stated in the model repository's introduction, compared to T5, FLAN-T5 is "just better at everything." With its permissive license, FLAN-T5 has become a popular option for a starting instruct model.
Orca is a descendant of LLaMA developed by Microsoft with finetuning on explanation traces obtained from GPT-4.
Orca-13B is a LLM developed by Microsoft. It is based on LLaMA with finetuning on complex explanation traces obtained from GPT-4. By using rich signals, Orca surpasses the performance of models such as Vicuna-13B on complex tasks. However, given its model backbone and the data used for its finetuning, Orca is under noncommercial use.
Further reading