Automounters are available on most unices (at least on all, that I tried). They provide access to file systems on demand, i.e. they mount a filesystem when it is needed and unmount it when it is not needed.
In Open Source there are two major implementations:
amd is a widespread solution, which is well documented (there is even a book published at Sybex; and since June 2004 they also provide commercial support), while autofs lacks such support and marketing.The autofs-automounter is based on a kernel module for high efficiency. The kernel module autofs itself is part of all Linux kernel distributions and is therefore available to probably all linux users (maybe they did not activate it during kernel build). Its major defiences are the lack of direct maps and cascaded mount trees. But I like it for something that is non-standard. autofs allows to reference programs that provide the input maps. (The automounter's ``fstab'' is called map for historic reasons concerning its NIS abilities.)