Cassandra versions & Builds
At any given time, there are a number of different versions available to install:
Cassandra stable releases are well tested and reasonably free of serious problems, (or at least the problems are known and well documented). If you are setting up a production environment, a stable release is what you want.
Download links for the latest stable release can always be found on the website.
Users of Debian or Debian-based derivatives can install the latest stable release in package form, see DebianPackaging for details.
Users of RPM-based distributions can get packages from [[http://www.datastax.com/blog/announcing-rpms-cassandra|Datastax].
Betas and release candidates
Betas are prototype releases considered ready for user testing, and release candidates have the potential to become the next stable release. These releases represent the state-of-the-art so are often the best place to start, and since APIs and on-disk storage formats can change between major versions this can also save you from an upgrade. The testing and feedback is also highly appreciated.
Nightly builds represent the current state of development as of the time of the build. They contain all of the previous day's new features, fixes, and newly introduced bugs. The only guarantee they come with is that they successfully build and the unit tests pass. Nightly builds are a handy way of testing recent changes, or accessing the latest features and fixes not found in beta or release candidates, but there is some risk of them being buggy.
The most recent nightly build can be downloaded here.
Cassandra's git repository is where all active development takes place. Anyone interested in contributing to the project should use a checkout of trunk. If you do run from git, be sure to update frequently, and subscribe to the mailing list to stay abreast of the latest developments.
Instructions for checking out the source code can always be found on the website.