A set of tools and libraries to access human-editable, plain text databases called recfiles. The data is stored as a sequence of records, each record containing an arbitrary number of named fields. They're basically flat files. Field names and types are specified with %, data is in field name: value format. It's sort of like key/value, but more structured. Fields can be mandatory or forbidden. Primary keys, unique fields, automatically incrementing counters and timestamps. Template support for running reports. SQL-like joins and foreign keys. Individual fields can be encrypted. Conversion to and from several formats.
A file based wiki that uses markdown.
Pepperminty Wiki is a complete wiki engine contained in a single file, inspired by @am2064's Minty Wiki. Upload to a PHP host and that's it. No database required. Uses Markdown. Has full text search and edit history support. Even has comments. Has a rudimentary API right now.
Personal bookmark service. Does not use a database. Can be run entirely privately. Has an API and a full-text search function. Very simple to use. Also lends itself to snippets, note taking, comments, hashtags. Offers RSS and ATOM feeds.