They're quite similar. Nexus indexes decentralized homeserver data and events into a fast social graph for pubky.app and potentially for other 'social' apps. But Pubky indexing is still forming: today’s social app-view is one path, alongside designs and plans for event and geolocation indexing, broad web URL crawling, personal indexing (in Atomicity). Also there are ideas for more generic aggregation and indexing, instead of only app-specific ones.
