Pesterchum is a messaging application from Homestuck, similar to AIM, Yahoo Messenger, or MSN Messenger. With it, the kids are able to talk to each other. To use Pesterchum, you must first have a screen name for it, called a "chumhandle." This name is a camel-cased combination of two different words, often based on the person's interests. Reed Majors' chumhandle is arcaneNotation, Luna Quinn's is westernLuminary, Drew Keifer's is digitalInfiltrator, and Theo Ryder's is stealthyInferno. Pesterchum is a bit quirky compared to other instant messengers in that the client itself is based on the word "Pester" which itself isn't exactly the kindest of words. All of the lines and syntax used in Pesterchum are based on this word, and its connotation is that of one being annoying rather than the light-hearted buddy system that other messengers typically have.
Pesterchum also features a mood system. In version 6.0, one can select from only six moods; Chummy, Chipper, Palsy, Bully, Peppy, and Rancorous. All these moods look exactly alike except for the angry red face of Rancorous. Pesterchum 7.0 has nine moods to choose from: Chummy, Mystified, Amazed, Insolent, Bemused, Pranky, Pleasent, Rancorous, and the ever popular Smooth. Unlike 6.0, 7.0 gives each mood its own facial expression. Changing the mood has little effect on when others pester you.
Along with having a chumRoll, each of the kids also has a trollSlum, which is a list of of Trolls with whom they might rather avoid speaking. The Trolls' IM software appears to bypass the block, however. The trolls are all in a Rancorous mood, though this may apply automatically to anyone in the trollSlum
The fans (specifically, Shinmera and Armada) seem to have created their own version of Pesterchum. The program also has a side version, "TinyChum", which is more compact than the original, and seems to have replaced the original entirely. A yet newer version has been created by another author and has been rewritten 'from scratch.'
NEWEST VERSION (3.41) by illuminatedwax.
Themes for 3.41, by ashdenej et al.
NEWER VERSIOn (2.5) by Grimlive95 and Syniphas.
FORUM THREAD (TINYCHUM & 2.0) by Shinmera and Armada.
There also happens to be a real, non-fan version Here.