There is also https://github.com/maximhq/bifrost which apparently overcomes some performance issues of litellm and is easy to get going.

Yeah they definitely belong in the same space. Nexus is an LLM Gateway, but early on, the focus has been on MCP: aggregation, authentication, and a smart approach to tool selection. There is that paper, and a lot of anecdotal evidence, pointing to LLMs not coping well with a selection of tools that is too large: https://arxiv.org/html/2411.09613v1

So Nexus takes a tool search based approach to solving that, among other cool things.

Disclaimer: I don't work on Nexus directly, but I do work at Grafbase.