ProjectLibre is an open source project management solution that is actually a fork of OpenProj (which hasn't been updated much since 2008). ProjectLibre is quite popular with over one million downloads since 2012, but as many free open source projects it is plagued with problems like terrible interface, lack of support and missing essentials, but its creators have managed to add Gantt, PERT Graph and Earned Value Costing. If you are looking for a free ProjectLibre alternative available both in cloud and as self-hosted software for on-premise deployment (sold with source code), Bitrix24 makes a great choice.
* Please note that the information may have changed since the publication. For current prices and features please visit Bitrix24 pricing page.