Google Wave was a pioneering collaboration platform that was unfortunately discontinued in 2012 (the product still exists as Apache Wave). Bitrix24 offers a number of advantages as Google or Apache alternative. First, there is a free cloud version. Second, Bitrix24 is available both in cloud or as self-hosted software that can be installed on your server (in which case you get access to open source code). Third, Bitrix24 offers a lot more collaboration tools that GoogleWave ever did. Finally, Bitrix24 comes with mobile apps both for Android and iOS, something that Apache Wave doesn't offer even now.
* Please note that the information may have changed since the publication. For current prices and features please visit Bitrix24 pricing page.