I am a Mathematica fan, after using it for months, the TI-83 plus can rarely feel the warmth of my hand1.
During school, or at friends house2, I have to deal with the life of Mathematicaless...
SpeQ come out of no where (well.. on stumble upon) and become part of my mathematical tool set!
First of all, SpeQ calculator's interface is command line like (btw, what is Microsoft thinking? calculator showing only one line of numbers?). Input and output, easily done.

Graphing, storing variables, add comments, declare functions and save the input+output are all possible.

The best of SpeQ is it's size! The main program is only 121KB, the help file is larger than the program, now I can take it everywhere, include my Journalism class, where the computers runs win 95/98 and the main portable storage device is floppy disks.
Did I tell you it's free?

1. 1. Replace "rarely" with "never" once Mathematica are allowed for all tests
2. 2. who does math at friend's house