how to laser printing postage with a linux system

[Josef Lowder]

I know that many people are now printing postage in any designated amount 
on their inkjet or laser printers, but I have not yet been able to find a 
place where I can do that with my Linux system.  usps.com apparently only 
offers printing postage for priority and express mail, while stamps.com and 
endicia.com and others apparently only work with M$.  Also, some 
systems apparently require a monthly fee and special software. 

Is that all there is?  Any suggestions how to do this with Linux and 
without extra monthly fees and special software?