I think this is the first HL2 mod so far.
http://www.filespace.ru/Games/Half-L...Thing.rar.html
Found a link to this on a Hungarian HL site. Its in Russian, so heres what the fish has to say about it.
""
The modes of in no way large, it consists of ya-ekh of maps (3- small of map and 1 large). To pass it to you will not compose large labor, I think the maximum of 30 minutes of play time, but that is less. A little about the subject: You certainly call Gordon Freeman you you work not known at what plant in the laboratory which it is located on levels and they suddenly to you report that at level 2 it occurred what that emergency, and you they request about the aid, in reality at level 4 (zasekrechenyy sector, guarded by soldiers) occurred unsuccessful experiment, and as a result for the freedom was pulled out the &.tsuot;NEccTO&.tsuot itself;. And here you as the respectable worker of this ill-starred plant go on you pomosh' into the shop of №2. well and then it went it went, on the way you meet everyone to nechest' which it were escape from the underground laboratories, as a result not of successful experiment. By the way at the end you will see that peasant himself which all this it did devise, to me it is very it's a pity? but you will not be able to kill this evil uncle.
""
So its four single player maps, about a half-hour of play time.