Collagene is a cloning software that is no longer actively maintained. It has however a solid code base and if you want to come up with new methods, or automate certain steps, it is a great foundation. It still probably has the best visualization system, even compared to Benchling and SnapGene, but lacks cloning features such as Gibson assembly.
Mac users are likely to have problems! Check out this link on running unsigned software to overcome this problem (if someone with a mac could help us sign the software, it would be great).
Download
Binary releases:
If you are interested in the source code, proceed to GitHub. There is also statistics on OpenHub.