The easy answer is there is no competition. ;-) Omeka’s mix of ease of use, focus on presentation and narrative exhibition, adherence to standards, accommodation for library, museum, and academic users, open source license, open code flexibility, and low ($0) price tag really make it one of a kind. If you are a librarian, archivist, museum professional, or scholar who wants a free, open, relatively simple platform for building a compelling online exhibition, there really isn’t any alternative