I'm in a slightly different scenario (Civil Engineering rather than Software), but I think there's similar tendencies.
I think increasing work variety is one of the things that would encourage people to stay, but kind of doesn't keep in line with what employers want. Employers generally want specialised people that are really good at the individual thing that they do. Employees on the other hand want to be able to try new things and work on different types of projects.
The other thing is giving people more autonomy (I think that's the right word...) to work on projects that they're really interested in. Google are a prime example of this with 'Google time' if you want to look into it, where essentially employees can work on whatever they want for 20% of their time (and sometimes they just choose to keep working on whatever they were doing before), but giving people more flexibility to work on their own side-projects can keep them much happier.
I'm in a slightly different scenario (Civil Engineering rather than Software), but I think there's similar tendencies.
I think increasing work variety is one of the things that would encourage people to stay, but kind of doesn't keep in line with what employers want. Employers generally want specialised people that are really good at the individual thing that they do. Employees on the other hand want to be able to try new things and work on different types of projects.
The other thing is giving people more autonomy (I think that's the right word...) to work on projects that they're really interested in. Google are a prime example of this with 'Google time' if you want to look into it, where essentially employees can work on whatever they want for 20% of their time (and sometimes they just choose to keep working on whatever they were doing before), but giving people more flexibility to work on their own side-projects can keep them much happier.