Yes, in its most basic configuration, it is essentially a microprocessor trainer! The only I/O you had was a set of 8 "sense switches," which were a byte-wide input port, and those were shared with the upper 8 address bits. Someone eventually figured out routines that make use of nonexistent memory in the base configuration to use the upper address lights as a "display," by writing loops that accessed those areas frequently enough to make the LEDs look illuminated due to persistence of vision. That, with the sense switch inputs, was used to put together a "Kill the Bit" game!

There was another "output device" discovered in the basic configuration: RF interference! Someone was listening to an AM radio while hacking on their Altair, and noticed in some parts of the program they'd get a ZIIIIIP! sort of noise out of the radio, when the cover was off. This was hacked on and expanded into a tune-playing program! Naturally, one of the first songs the Altair was taught to "sing" was "Bicycle Built for Two" ("Daisy"). Here's a video of a friend of mine's Altair running the music program:

https://www.youtube.com/watch?v=tImrHlYLzZo

He'd brought his recently-acquired Altair 8800 over to our house to get it running, since I had a lot of other S-100 stuff going. The terminal to the left of it was running a ROM monitor on a Dajen SCI board, described here:

http://users.glitchwrks.com/~glitch/2011/11/03/dajen-sci

...after painstakingly toggling in the music program through the front panel, we used the Dajen board to burn the program into a 2708 1K x 8 EPROM so we wouldn't have to do it again!