I've been toying around with making a version of femtoBASIC in PropBasic instead of spin for speed.
Here is my first crack at it.
The hard-coded program has a tight 3 line loop that toggles pin 0. It's pretty fast 300,000 (simple) lines per second. So the pin toggles at 100KHz. [edit speed is quite a bit slower now]
I'm sure when I start fleshing it out, I'll need to switch to LMM so that will make it quite a bit slower (about 75,000 lines per second).
I uploaded a new version that uses LMM, speed is about 57,000 (simple) lines per second. Editing the program now works too.
 July 5, 2010 uploaded a new version. Math works but strictly left-to-right evaluation. No "IF" or "FOR" yet. But it's getting there...
 July 7 2010 uploaded a new version. Simple IF ... THEN line# expressions work now.
 July 12 2010 uploaded new version. Added PEEK, POKE, DEBUG, INKEY, DISPLAY, VARS, NEW
 Dec 22 2010 uploaded new version. Added GOSUB/RETURN, FOR/NEXT, and more.
 Dec 23 2010 uploaded version 0.02 Dec 23, 2010. Added LOAD and SAVE.
 Dec 25, 2010 updated version 0.04. Added multiplie commands per line seperated by ":". And READ DATA RESTORE.
 Jan 9 2011 updated version 0.05. Added NTSC display, PS2 Keyboard input. Added LOCATE command. Allow lowercase.
 Jan 12 2011 update version 0.06. Various fixes. Allow IF...THEN commands.
 Feb 1, 2011 allow 8 character variable names (except FOR..NEXT). PLOT, LINE, etc.
 Feb 4, 2011 Full expression evaluator (Thanks Mike Green). Added system variable CHARS to change the bitmap of characters. POKEB CHARS,255 changes the top line of the space(32) character to a solid line.
 Feb 5, 2011 Fixed pin ranges, RND, ABS, backspace at start of line.
 Mar 9, 2011 Updated to version with color video.
 Mar 11, 2011 Updated. Changed name PEBasic (Propeller Embedded BASIC)
 July 11, 2011 Updated. Posted version 0.16.