reegle (lower-case) was a search engine specifically covering the fields of renewable energy, efficient energy use, and climate change issues.

It was developed in 2005 by REEEP and REN21, with funding from several European government agencies.

[3] It was conceived as a public resource for governments, project developers, banks and finance institutions, NGOs, and international organisations as well as the general public.

The central function of the site was a search engine, which offered a "mind map" based search refinement function.

The website offered an online glossary covering about 4,000 terms from the clean energy and climate sector, with definitions from Open Data sources.