These are online games for BBS's I wrote in the late 80's to mid 90's. You can download and try them out yourself, or if you have a BBS you can run them for your users (please let me know if you put these on a BBS!). Though they were designed for BBS use, they run fine locally, though the experience is not quite as authentic. They'll work fine under DOS, a Windows command prompt or even a DOS emulator on linux.
Blastem was my first real attempt at an online game - a real time action/arcade game for BBS's - written with Bruce Mills (who did all the "artwork" including 360 different screens). This was quite difficult considering a 2400bps modem was typical at the time I started it. You wander around a city that's been taken over by aliens - blasting them, picking up upgrades for your "mech", getting credits for kills & buying better stuff & so on. The further away from the starting point you are, the harder & faster the monsters get so the more skill & equipment you need. There are lots of different weapons - lazers, missiles, death-blossoms, freeze bombs, nukes etc.
Silly snakes is your basic snake/nibblies derivative turned into a real-time online BBS game. It has 16 levels of increasing intensity from trivial to near-impossible. Just for something different, the snake wraps around the edges of the screen, and you need to use this feature on several levels. It runs at full speed on a 2400bps connection!
Kill things was basically an experiment to see if it was possible to do a multi-user real time action game on a multi-line BBS. Basically, you just run around killing other players and see how many kills you can get. It works quite well considering its simple messaging system - r/w to a common file - with up to 4 players at once. You can also write short messages (insults usually) to each other while playing. Fighting inherits the lazer & death-blossom weapons from Blastem.
BTW, the game is not very interesting for one player :-) (to see how it works multiplayer, try loading it more than once in separate windows with each as a different node)