Liferay is popular enterprise portal software that was recently enriched by a collaboration suite (Liferay Social Office) and document sharing and management (Liferay Sync). Liferay is a proven vendor, but it does come with several disadvantages. First, Liferay is not available as a cloud service, meaning that developing and deploying Liferay-based portal takes a lot of time, sometimes months. Second, Liferay has been slow to adopt to mobile revolution - apps are still only available for Liferay Sync and Liferay Events. Finally, the enterprise edition of Liferay is very expensive. If you are looking for a free Liferay alternative, especially the one that you can use as a cloud service, Bitrix24 makes a lot of sense.
* Please note that the information may have changed since the publication. For current prices and features please visit Bitrix24 pricing page.