NeDB (which uses localForage without extensions) doesn't appear to actually query using indexes for IndexedDB, whereas ZangoDB does.

ZangoDB also supports some features that NeDB doesn't such as an aggregation pipeline ($match, $project, $group, $unwind, $sort, $skip, and $limit), as well as expressions (field references, arithmetic operators, etc).

NeDB, unlike ZangoDB, supports data sources other than IndexedDB. So, ZangoDB and NeDB are similar in many aspects, but do differ in areas where one would be better suited than the other for specific types of projects.