<p>I am looking for a lean and well constructed open source implementation of a B-tree library written in C. It needs to be under a non-GPL license so that it can be used in a commercial application. Ideally, this library supports the B-tree index to be stored/manipulated as a disk file so that large trees can be built using a configurable (ie: minimal) RAM footprint.</p>

<p>Note: Since there seemed to be some confusion, a Binary Tree and a B-Tree are <em>not</em> the same thing.</p>

The author of the
SQLite implementation
has disclaimed copyright.  If LGPL is okay, then maybe you could use
GNUpdate's implementation
?