Here's the list of tools which you can use to facilitate the Lightning migration journey
Key feature: Link to all the tools for all checks in one place
Key feature: We can customise the Welcome screen in Lightning Screen as per customer requirements
Key feature: Conversion of classic type of documents into Lightning friendly docs
Key feature: Conversion of classic button/links to Lightning Actions
Key feature: Report to improve implementation for e.g highlights unused components.
Key feature: Track adoption and usage of Lightning Experience
Key feature: Help in change management from Classic to Lightning
Key feature: Calculate Increase revenue and reduce costs by switching to Lightning
Useful Link: Lightning Experience Transition Tools here