Tartan is a text parsing engine targeted at wiki text. The syntax specification is defined in YAML in the form of regex-based rules. It supports layering and multiple output types. Rules for Markdown to HTML are included, with optional layered extensions for tables. It is implemented in Ruby, but looking to have implementations in other languages.
nessus-xmlrpc is a Ruby library for the Nessus XML-RPC interface. You can use it to start, stop, pause, and resume scans. It lets you watch progress and status of scans, download reports, etc. It comes with an example command line program that shows how easy it is to interact with the Nessus scanner.