By now there is a considerable amount of WordPress code around that is meant to be re-used by other developers. Unfortunately there is little to none practical and solid information on it and generally you are stuck going through frameworks one by one until you find the first you like or think they all suck terribly (whichever comes first).

Let’s make community writeup on which frameworks and parent themes we really use and why.

Please include:

• purpose (parent theme, theme framework, helper code, etc)
• strong features (which make it interesting and useful)
• downsides (what it does inconveniently or different from usual)
• licensing and pricing (if not free)

Hybrid

Theme Hybrid, developed by Justin Tadlock. Scope of code is primarily PHP internal functionality and front-end templates for themes.

Interesting features:

• code aims to minimize template edits, most of functionality can be controlled via hooks;
• context-aware – extended body-class, dynamic context-aware hooks that allow to hook events that fire only in specific context;
• tightly integrates with several generic and Hybrid-specific plugins from same developer;

Issues:

• backwards compatibility can be an issue, especially if trying to use older child theme releases with newer parent theme.

Pricing:

• all code is freely available, under GPLv2;
• access to support and non-basic documentation $25/year.

There is range of releases for different stages of development.

Hybrid Core

Standalone framework for developers making their own parent themes. Highly modular with most of the features loaded on demand by custom add_theme_support() calls.

Hybrid parent theme

Long established parent theme (earlier versions were from before standalone Core release). Includes considerable amount of ready-made templates with more available for download separately.

Has multiple child themes available (both native and from other developers).

Prototype parent theme

Latest cutting edge release to show practical usage of Hybrid Core.