There is to my knowledge no product that Microsoft makes that does not have an alternative. Here are some of the main ones:

High-end PCs preloaded with Windows. Anyone with a budget of greater than $1500 should consider a Power Macintosh. For budgets of $1000 to $1500 the Macintosh is still an alternative, but a less attractive one.

For PCs under $1000 or laptops, Linux is the most logical choice.

For people who only want to play games, a games machine might be the best bet.

Spending $100 on a good quality modem and using an existing 486 is a very good alternative to buying a new machine if the sole intent is internet access. Linux does very well on these too-slow for Windows machines. (Make sure you have plenty of RAM and swap space if you're going to use X).

Router / firewall use may be a good way to get new life out of a 386 or 486 if you've already purchased a new machine.

Star Office is a viable replacement for Microsoft Office, and also has its own browser.

Netscape Communicator is a good replacement for Internet Explorer and Outlook Express. Though slower than IE, it lacks a lot of the security holes that IE has. Most notably, Java and JavaScript can be turned off for security conscious enterprises. Opera is available for a wide variety of platforms, and Linux users can avail themselves of KDE Konqueror, which is a good fast browser with frame support. Konqueror does not support either Java or JavaScript which make it a good candidate for security-conscious workplaces where such ability may not be desirable.

Linux Servers are a viable alternative to NT and 2000 servers, especially for small server and web hosting. For Enterprise Level computing, consider a commercial grade Unix such as Solaris, HP-UX, AIX, etc. Of course for something high-level like a DNS server on the Internet, I personally wouldn't dream of anything short of a high-end Unix that supports as many processors as possible.

Sendmail, postfix and a host of other programs can replace Microsoft Exchange. For those looking for a commercial product, try HP Open Mail.

Linux can do a host of things thought reserved for Microsoft -- including DHCP and BOOTP services, SQL, etc. And you can get the benefits of a secure operating system for much less money than you would spend on NT or 2000.

Apache still commands a majority market share for the web server market. Microsoft has a number of extras with its Internet Information Server, but these are being duplicated in the Unix world with Java Server Pages and Java Servlets. And let us not forget the Macromedia Flash plug-in and CGI (Perl) scripting.

Real Player is still the dominant choice of websites over Windows Media Player due to webmasters' unwillingness to offend the users of alternative operating systems.