I am looking for any available tools that will group drugs by their mechanism/mode of action (MOA/MoA)? For example, a list of all drugs that work on the mu opioid receptor, along with some measure, perhaps a transcriptional measure, of how prominent that MOA/MoA really is as any drug is likely to have multiple MoAs.

Please do not mistake this for a tool that takes a single drug and derives nearest neighbour clusters based on their MOA/MoA. I know these exist e.g., Mantra 2.0 for MoA.