Depending on whether you use SFU or SUA, the tools will either be bundled into the installation package directly (SFU), or will be downloaded from a Microsoft repository as part of the installation process (SUA).
Interop Systems, a third-party company that was founded by some of the original employees of Softway Systems, also maintains ports of several common open-source applications. Some of the packages are simply updates to the utilities that are bundled into SFU and SUA, but Interop Systems also maintains ports of other, critical applications like OpenSSH and Apache, among others. Interop Systems charges a one-time fee of $20 for access to its repository of ports, but the cost is well worth it.
You can also try your hand at porting applications yourself, using the bundled development tools (or the updated versions from Interop Systems). In my experience, this can be done for some things fairly easily, while other applications are extremely difficult to work with. Generally speaking, if the source tarball uses GNU configure scripts that support Interix as a platform, and if the application does not expect to work with Unix-specific resources such as /etc/passwd directly, then you have a pretty good chance of being able to successfully compile the application, although it still may not run. If the application is written to specific target platforms and it does not have explicit support for Interix as a target, then you are probably not going to get it working unless you spend a fair amount of effort on hacking the code.
As a quick sampling of the feasibility here, I was able to get the latest version of Berkeley DB to compile and run without a problem, and I was also able to get some OpenLDAP tools to compile (but not all of them, and the winners did not run fully). I was also able to get SpamAssassin and some support modules to compile and run (including Net::LDAP, although I had to upgrade Perl from Interop Systems' repository first). A few other Perl modules would not compile or would not pass the "make test" phase. Nor was I able to get the CMU SASL libraries to compile, while UW IMAPD and Cyrus IMAP are written to specific platforms that do not include support for Interix, so I was not able to compile those either.
As for my specific usage needs, the only two Unix applications that I really need for this system are OpenSSH and Squid, and I am easily able to use Windows services for everything else. In some cases, like printer management, I am far better off with the Windows services. Since Squid and OpenSSH are available from Interop Systems in pre-built form, my needs were met easily. In short, I'm able to run best-of-breed open source applications under Windows just as if they were running under Unix, and am also able to benefit from tight integration with the Windows environment.
