Someone wanted a summary posted.  I'll do what I can:

1)  sc.   This is a standard free unix spreadsheet.  Reasonable power and 
features, but lacks some common features (like sorting) that you would expect,
and the command syntax takes getting used to.  Like many older unix programs,
it doesn't use the features of a modern keyboard, and so commands tend to be 
keystrokes.  To enter characters in a cell, you need to go to insert mode.

Most keybindings are vi-ish.  No graphs.  Works better in some terminal types 
than others.  Stable, though.  Comes with a parser to import from other ascii
formats.  Output to plain text, or colon-separated table.

Current version is 6.23 I think.  Comes with slackware.

2)  xspread.  The latest versions of this are extensions of sc-6.2*.  
Understand the mouse pretty well, and has some graphing capabilities (like
bar graphs of data, etc.)  Still has some ``mode'' issues, in that if you click 
the mouse on a cell, it is not by default in `input' mode.  Commands for 
editing cells are from sc.  Some lotus-like extensions of sc sommands, and 
a command menu.  No X cut&paste.

Version number:  I have 2.3, which is based on sc-6.21.  There may be a newer 
one.  Hard to find on the net, but at least a fairly recent version is in 
slackware.  

3) ss.  An sc variant, with more lotus-like commands.  I like it better than sc.
Nice output options.  Can output into TeX, troff (I believe), etc.  Better 
cell-editing options than sc.  No graphics that I know about.  Same importing
capabilities as sc.

I have 1.33.  I think it's more-or-less available, but I got it from someone
else through e-mail.  

4)  oleo.  This I know nothing about.  It is supposed to be powerful, but is
like emacs in that it takes some work to use.  I hope someone can provide more 
information.

5)  table. Part of the auis-wp package.  Integrated with the rest of the Andrew
stuff, allows the use of formatted text, equations, and graphics as cell 
contents, and allows a working spreadsheeet to be part of an ez document.

There is a good (and customizable) menu of options, and on-line help.  File
save format is a tab-separated ascii file, with embedded strings top and bottom
for cell size, etc.  No importing capabilities that I can figure out; you need 
to put it in that format (it'll add the embedded commands).

There is a thing that lets you have as range of cells bar graphs and the like, 
but it doesn't have real graphing capabilities.

Functions are more limited than sc and its clones.  Cell addresses are a pair of
numbers rather than a letter-number combination, so no formulaic compatibility 
with sc or lotus (many formulas in lotus-123 are the same in sc, etc.).  Some
obvious statistical functions are missing.

Cut and paste of cells is well-managed, and it uses the mouse well.  In fact 
you must use the mouse to navigate (for Pg-up and Pg-dn, for example).

Bugs:  I can't change the default display font, and printing is only 
double-spaced.  There are display problems with the row numbers obscured by 
the window border.  I have heard that the spreadsheet size is limited, but 
managed to keep a whole year's worth of checking account activity on it.

That's all I know anything about.  There is also another variant of sc, I 
think called slsc ??, built independently of the curses library, but it 
seemed to have only a small subset of sc's commands.  Perhaps someone else can
sing its praises.