NSSM - the Non-Sucking Service Manager
nssm should work under Windows 2000 or later. Specifically, Windows 7 and Windows 8 are supported. 32-bit and 64-bit binaries are included in the download. Most of the time it should be safe to run the 32-bit version on 64-bit Windows but in some circumstances you may find that it doesn't work and you must use the 64-bit version. Both versions are compiled from the same source code. If one works for you, use that one. If it doesn't, try the other.
Source code is included in the download or you can browse gitweb.
You can also clone the repo from git://git.nssm.cc/nssm/nssm.git with git.