We're currently integrated (embedded experience) with the 2 leading eSignatures solutions : DocuSign & HelloSign.
You've mentioned several times DocSketch so this is on our roadmap now.
An integration between Clust DocuSign or HelloSign requires a Gold Clust account and an API oAuth embedded Account at DocuSign/ HelloSign.
💡You can use Clust tasks to redirect recipients to your current eSignature public template if you have one so you don't have to make the integration.
PS:Our own signature is on its way.