Nexus is an artifact repository. It has lots of features but so far as I can tell it’s principally interesting for two reasons:
1) it acts as a maven repository to which your build server can publish artifacts
2) it acts as a caching proxy for any number of remote repositories

1 means that I don’t have to pull the code and build the libraries from all the other groups in my organization when all I really want to do is build the main app and link in their stuff. That’s great when engineering has like 300 programmers, but maybe not so interesting when there are only 2.

2 means that all those weird repos hosted on DSL in some eastern European country can be mirrored in the corporate repo and the artifacts only have to be fetched once.

TeamCity is a build system, like Jenkins. From my hour of fooling around last night, it seems easier to get up and running than Jenkins, and it’s really easy to get it naively integrated with our GitHub repos. I suspect it will be way trickier to get it configured to watch “dev” instead of “master”. There’s also a plugin for IDEA that integrates IDEA with TeamCIty and I haven’t poked at that yet so I don’t know what-all is available there. Maybe something interesting, or maybe just agile bogosity.