Ollama is llama.cpp with a nice little installer GUI and nice little server binary.
llama.cpp has a server binary as well, however, no nice installer GUI.
The only time recently Ollama had a feature llama.cpp didn't was they patched SWA in with Google, llama.cpp had it a couple weeks later.
Ollama is significantly behind llama.cpp in important areas, ex. the Gemma blog post, they note they'll get on tool calls and multimodal real soon now.