What strikes me as odd is people wanting to write things that traditionally are written in C/C++ and more recently also in Go/Rust/Java/D in JS. The reason these arguably slower, in development speed, languages are used for things like DBs is that they are write once re-use thousands of times, and this use case warrants being slightly lower level and less rapid in development and gaining performance and I would argue maintainability.
 Note: In case you are wondering why I dislike JS: 1. JS's extensive use of spaghetti cough I mean callbacks 2. Higher effort needed to use compute resources for a single task in a parallel fashion compared to other langs 3. I dislike dynamically typed languages (I belive they are harder to maintain) 4. Performance: http://benchmarksgame.alioth.debian.org/u64/benchmark.php?te...
While I understand that packaging motivation; it seems to me to be less relevant due to msi/rpm/deb packages. Those technologies make it pretty easy to package an application built with heterogeneous components.
It's true that it's easy to package such applications for unix systems, but it's much harder on Windows. What makes Node Webkit great is the fact that it's cross-platform with very little pain, and in that case having the DB in the JS code makes packaging a breeze.
I should note I know people who make this choice. They can write these things in C, and in the past, they have. But they are choosing Node.js. So it's not just a "what you know" affect.
a) and b) The database is loosely coupled with the query language implementation, so it could be possible to change the query semantics without breaking it. That said I have other priorities for now (some adaptation for Node Webkit, porting it to the browser).
c) NeDB queries return vanilla objects or array of objects , on which you can use all the underscore functions you want.
d) Depends what you want to do. If you want to write a REPL I think it shouldn't be too difficult, and it may be a good idea to do one. In the meantime, since the API is the same as MongoDB's, you can learn NeDB using MongoDB's REPL :)
Amongst those are a native SQL engine (sqlite) and a native NoSQL engine (levelDB, through the IndexedDB API)
It'd be useful to know what benefits NeDB brings over other existing storage mechanisms.
But if you need multiple programs to use your DB at once you need a more powerful solution such as MongoDB. The goal of NeDB is to bring DB features to desktop apps or low concurrency webapps, not replace Mongo and the like.
And append-only doesn't make you immune to corruption. There's still a possibility of two processes writing at the same time corrupting what gets written to the file.
If it is, you should probably put a larger warning about dataset size than the line you currently have :)
As an aside, I'm considering enabling large datasets for NeDB as some users asked, but that would be a lot of work so I'll wait for more requests.
At first I was trying to think of words that start with "ne-" before I clicked through and realized "E" stood for something on its own :-)
You can use that once you've outgrown NeDB.