This is a free metadata indexing system developed in PHP. OHS (Open Harvester System) is an Open Source PHP search engine. It indexs and creates searchable listings of metadata from Open Archives Initiative (OAI)-compliant archives.

OAI services include sites using Open Journal Systems (OJS) or Open Conference Systems (OCS).

Features of Open Harvester System:
- Ability to harvest OAI metadata in a variety of schemas (including unqualified DC, the PKP (Open Journal Systems/Open Conference Systems) Dublin Core extension, MODS, and MARCXML). Additional schema are supported via plugins.
- Flexible search interface that allows simple searching and advanced searching using crosswalked fields from all harvested archives. Advanced searching of archives that share the same schema will be possible using fields as defined in the schema. When creating crosswalks for searching, admins can define elements are text, date, or HTML multiple select interface widgets.
- Ability to perform granular harvesting using setSpec and timestamps.
- Ability to perform post-harvest and pre-indexing filtering/normalization on metadata.
- User Interface with CSS and template-based HTML for easy customization.
- Searching is highly scalable (creates an inverted index for searching).

Requirements:
- PHP 4.2 or Higher
- MySQL 3.23.23+ or PostgreSQL 7.1+
- Apache 1.3.2x or Microsoft IIS 6+