There's an old saying, "more than one way to skin a cat," but with law-firm specific technology there really aren't too many ways.
Of course, there's the ubiquitous standard software used by nearly everyone in the business world (e-mail, word processing, spreadsheets, etc.) that I won't dignify mentioning by name. BigLaw, like any other major industry, has for the most part adopted them.
What's interesting, though, is that for such a large industry, there is a shockingly small number of law-specific programs commonly being used. Plus, there isn't much variation in the features between competing software packages. After learning one set, it's common to move to another firm and find either the same set or a comparable version of it that's easy to transition into.
Of course, trying to convince your new employer that you already know how to use their billing or e-discovery programs isn't so easy. They still insist on spending days (if not weeks) training you regardless of the fact that you may know more about it than the IT department's instructor does.
Guess where I've been? Yep. Being re-trained in programs I've used since this instructor was in junior high. Instead of in my office doing work. Serious. Waste. Of. Time.