Best use of ob_, custom error handling, and variable variales evar: simple templating.
includes $filename and renders its output to the return value. $locals, if used, will add a set of variables to the included context.
Same as above, but allows you to define a base template folder and omit the .php - just for cleaner code.
Same as Parse, but any output between the opening call and the closing call (no arguments) will be buffered intot he $content variable of the template.
Play around with t(..) to find out more; I don't feel like documenting it.
Log4J is a really nice Library that aims to facilitate outputting debugging information, but also relevant data, in Java applications. It is highly configurable, using both Categories and Class-Based rules, so that developers can narrow down the problems very well when debugging applications.