Cliff's right - the file at
http://www.fish-byte.com/MA3Beta.zip will always be the very latest (often highly experimental) version. The file contained in the ZIP will always be called MA3Beta.scr, and will overwrite any older file of the same name (so if you want to keep an older file, you can rename it).
When you run the program, the version number will be in the Statistics text in the upper left corner of the screen. This display can be toggled on and off with the "S" key.
Edgar is working on making Beta10a the official version on SereneScreen.com.