CoCo2 for the Commodore VIC-20 is a really neat tool for creating your own games, similar to SEUCK for the Commodore 64, but much simpler.  Requirements are at least 24k RAM.

Included in the archive is the reference manual, and 3 demos on the program disk.

Link to the manual

How would you like to be able to use single-key entry for 52 BASIC commands? With ''VICword" running in your VIC, you can hold down the SHIFT key and hit the letter "L" and the word "LOAD" will appear on screen. Hold down the COMMODORE key and hit "L" and "SAVE" writes itself on the screen. Especially helpful when typing in those long BASIC programs, VICword is a clever machine language program that puts itself into memory (expanded or not), protects itself from interference by BASIC, and then tells you how to tum it on or off  whenever you want.

This program comes from the book "Compute's Second Book of VIC" which you can find here or here.