Billy Wilcosky:

Flat file web software is about having a set up which doesn’t use a “traditional” database. Instead it uses plain text files, other files, and/or maybe something like a json feed to store the data.

In this post, he explains why he thinks flat file web software is on the come up (again):

Flat file software can be powerful. Depending on what you need. And I think with the right developers and brain power behind the movement it can be more scalable and secure. The sky’s the limit. When I hear a developer saying, no, flat file isn’t good because… really all I’m hearing is they don’t want to change the way web software works. Because what I’ve found is most anything is possible.

Here’s a couple of flat file platforms which are incredible. One is a CMS/blog, the other a forum. Yes, a flat file forum.

A somewhat-related categorical question: Does SQLite count?