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.
Released alongside Vicuna, Koala is one of many descendants of the Meta LLaMA model trained on dialogue data collected from the web. On the developers' benchmarks, Koala outperforms its sibling Alpaca, though its adoption has been significantly less than that of its other sibling, Vicuna. Due to its use of LLaMA, only research use is permitted.