I can think of a couple cases of genuinely communal women's work in the Middle Ages, in the sense of a group of women working together. Especially in Germany, women would have "spinning bees", where they would talk and gossip while they worked. (Civic authorities noted these as hotbed of dangerous religious discussion during the early Reformation). And in monasteries and quasi-monasteries, the working period would often feature sisters working side by side (albeit silently) at tasks like embroidery of altar cloths and vestments, or composing manuscripts for their own house or for a patron.

Then there are situations where women would be working side by side, but not at traditional "women's work." There were women day-labourers on construction sites and of course in farm fields. And in late medieval cities, as the "nuclear family/business" model for artisan labor grew prominent, the wife and daughters of a master craftsman would frequently be "unemployed employees," delegated particularly tasks as either support (food, cleaning, customers) or regular labor alongside hired help in professions from printing to painting.

A third subset of women's labour that could be done communally in some circumstances is what Merry Wiesner-Hanks has termed "support." That is, smaller-scale tasks that city authorities considered beneath their regulatory notice, because the income was petty enough to "support" e.g. widows/add a little extra cash for a family with a lot of young kids to feed, but on a larger scale would ape a regulated and male-dominated trade. The most famous example here by far is candlemaking: pre-Reformation (and ongoing in Catholic areas, of course), women were the dominant makers of devotional and memorial candles for churches. (Think of how today, if you go to a "tourist destination" church, you can light a candle and say a prayer intention in exchange for a 50 cent donation or whatnot). In late medieval English parishes, candlemaking could even be an official responsibility of the parish women's confraternity.

Based on your remarks in the other thread, though, I suspect what you're most interested in is regulated labour (I am avoiding the term "organized" here because, whatever Ken Follett might have you believe, medieval trade guilds were not modern unions), and specifically, in trades that were dominated by women. Unfortunately, the narrative here for women as a class is bleak. As the scale and potential profitability of a task traditionally performed by women increased, men flocked to the work and--first practically, but by the end of the Middle Ages legally--excluded women from independent involvement.

The most (in)famous medieval illustration of this phenomenon, thanks to the seminal work of Judith Bennett, is women's involvement in brewing in late medieval England. For most of the Middle Ages, the favored daily drink of families who could afford more than water (the beggar's and penitent's drink) was a weakly alcoholic but flavorful and calorie-containing ale. Ale was typically brewed at home, by the household's wife/mother, for her own family's use. However, if a family needed some extra income, the woman would increase production for a little while and sell the extra. Word of mouth, merchant carts, and street signs would help direct potential buyers to the place where they could get some for their own family today. But with the introduction of hops to England, and the stronger/better-tasting/longer lasting (ergo, potential for larger scale production and profit) "beer" to England, the task fell more and more into the hands of men. Men ran and owned the larger, more collective labor-requiring proto-breweries. Women petty-scale brewsters lost an important revenue stream for their families and means of economic independence and public contribution for themselves.

However, there were a few exceptions to the general decline in women's participation in a trade as it grew more popular and eventually regulated. This seems to have been especially the case in the Low Countries/northern France and a few cases in early modern Spain, and the trades involved are very predominantly textile-related.

We are not talking here about separate women's and men's guilds for the same trade. (There were also a few genuinely mixed-gender guilds; I don't just mean widows of former master craftsmen who inherited their husbands' business allowed to join so long as they didn't remarry/with the understanding they would eventually marry a guild member and then the business would pass to the man). That would undermine a key characteristic of the corporate bodies we call "guilds": monopoly over the trade within city limits.

Other big-deal provisions were: first, the right to judge admission to and advancement in the trade. Who could become an apprentice, when an apprentice became a journeyman, who could become a master, who could then take on an apprentice. Second, guild officials had the responsibility to ensure quality control in the output of the trade, and punish members whose work fell short of the standard. (Guilds also had a variety of non-industry roles in urban society that were crucial to their function within the city, especially urban religious life, such as sponsoring religious drama productions every year that were HUGE events for the city/its parishes).

As Susan Broomhall showed in her studies of the women's guilds in Rouen and beyond, women's guilds were absolutely guilds in that respect. They regulated admission to and advancement in the trade, including kicking out apprentices who weren't good enough and censuring masters who abused their apprentices beyond what was considered good teaching practice. They had a similar internal organizational structure of officers in charge of overseeing members and relating to the civic government. Broomhall points out a key difference between the women's-only guilds of Rouen and those of e.g. Paris (as studied by Judith Coffin). In a lot of cities, women's-only guilds were also concerned with the moral (read; sexual) conduct of their members, trying to preserve the reputation of their trade and its artisans as wholesome. Rouen's female guilds show no signs of such concerns. This might indicate a greater acceptance for women workers in those particular trades in Rouen--the guild's beadles (officials) did not have to be concerned that scandal would push the city to yank away their corporate rights.

One final point I want to make here is, the overlap between "textile trade" and "women's work." There is a strong and longstanding link in the medieval European imagination between women and textile work. The "women's symbol" is even the distaff, used in spinning--the Distaff Gospels are this awesome satirical and vaguely misogynist 15C collection of real and fake proverbs supposedly told by women sitting around spinning (and clearly written by a guy). In less urbanized places and times, making clothing was a ground-up occupation done either in-home or on a loose specialization/informal basis within villages. Specialization in trades within villages is a lot more common at an earlier date than people today sometimes imagine. Spinning yarn into thread, weaving thread into cloth, sometimes fulling the cloth, making cloth into clothing, etc.

But by the time we get to later medieval cities, especially in Europe's industrial heartland (the Low Countries and environs--basically what we're talking about here), the range of textile trades was enormous and highly specialized. Rouen and Paris, for example, both had separate female guilds for draping (making clothes out of) new, linen cloth and secondhand, linen cloth (yes, specifically linen). Oh, and at least in Rouen, those two guilds basically hated each other and tried to get each others' members convicted of business fraud more than occasionally. The women's guilds also prosecuted men's guilds and individual male craftsmen they felt were impinging on their own guild rights (dyers, tailors, and of course merchants coming in for the most frequent hostility).

Broomhall makes one final point about the female guilds of 15th-16th century Rouen that pertains directly to your question. A lot of her sources are city court records, from guild officials' quick and frequent activism to defend their corporate rights against women and men alike in court. Broomhall wonders first if the guilds' apparently-unusual success in fighting back the tide of men's suppression of women's economic-industrial independence might relate to the Rouen guildmasters' judicial activity and skill. They were competing in the same arena, with the same tactics and goals as local men. But as she points out, there's no reason this particular trait should be specific to Rouen. What if our detailed knowledge of official, regulated women's work in Rouen is an accident of source survival? Maybe the role of women in regulated labor in other cities is either lost to the disappearance of sources, or waiting to be discoverd in town archives across Europe.