Alternatives for SSMS solutions & projects?
Reading between the lines, I guess the expectation/plan was for the SQL Server Data Tools (SSDT) project type to be extended to SSMS for the release of SQL 2012. Evidently that didn't happen, so we're stuck with the (frankly dreadful) SSMS interpretation of a project.

If you want something to manage your database source, you should be diving deep into SSDT. I'm currently using it for one greenfield project and also moving a large brownfield database to it. Minor niggles and pain points but no show stoppers and we're getting payback on the time invested already.

Jamie Thomson, who blogged extensively on VS2010 Database Projects (the predecessor), has started to publish articles on SSDT and appears to be as big a fan as I am. Bob Beauchemin is another early adopter worth following.  

If you want to organise a collection of random scripts (rather than a full database build) you can but support isn't quite "first-class". To do so, create a standard SSDT project type and change your scripts to compilation type "None" in the file properties.