A non-professional may sew normally on Chol ha'Mo'ed but a professional tailor may not sew in his normal method. (1)
According to Rebbi Meir a bed of ropes may be woven on Chol ha'Mo'ed in the normal method. According to Rebbi Yosi it may only be done in an alternative method. (2)
It is permitted to construct an oven or mill on Chol ha'Mo'ed but it may not be completes according to Rebbi Elazar. The Chachamim hold that it may even be completed.
It is permitted to cut the nails of a horse or donkey that is used for riding. (3)
Letting blood and all other medical procedures for animals are permitted on Chol ha'Mo'ed
Removing twigs from the land for the use of the twigs is permitted on Chol ha'Mo'ed but if they are removed for the purpose of clearing the land it is forbidden. (4)
It is permitted to slice dates on Chol ha'Mo'ed for the purpose of eating them but it is forbidden to press forbidden the purpose of sun drying them. R’ Papa permits pressing them because otherwise they will rot and it will be a financial loss.
Commerce is forbidden on Chol ha'Mo'ed unless there will be a financial loss. (4)
A BIT MORE
1. According to Rebbi Yochanan a professional tailor must leave gaps between the threads and according to Rabah Bar Shmuel he must sew uneven stitches.
2. There is a dispute between Rebbi Chiya Bar Aba and Rebbi Asi in the name of Chizkiyah and Rebbi Yochanan regarding the opinion of Rebbi Yosi. According to one opinion Rebbi Yosi permits weaving the bed only vertically and not horizontally and according to the other opinion Rebbi Yosi only permits tightening the ropes but not to weave it.
3. Rebbi Chama says that it is forbidden to cut the nails of a donkey that is used for a mill and Rebbi Yehudah disagrees.
4. If both the large and small twigs are removed form the land it is obvious that they are being removed for the purpose of clearing the land and it is forbidden. If only the large twigs are taken that they are obviously being taken for the use of the twigs and it is permitted.
5. It is permitted to collect a loan on Chol ha'Mo'ed if it would be difficult to collect it after Yom Tov because it is the same status as commerce that is permitted when there will be a financial loss.
Ravina asked Rebbi Ashi if it is allowed to collect his loans on Chol ha'Mo'ed and he answered since this is his only opportunity to collect it is similar to commerce that will result in a financial loss and it is permitted. The Ritva asks why Rebbi Ashi compared it specifically to commerce. It is not only commerce that is permitted, anytime there is a potential financial loss it is permitted to do a Melachah on Chol ha'Mo'ed. The Ritva answers that Rebbi Ashi is teaching us that even a small loss is enough to permit a Melachah on Chol ha'Mo'ed just as commerce is permitted even if it is to avoid just a small loss.
All commerce is forbidden on Chol ha’Mo’ed no matter how small. Both buying and selling is forbidden, however if the prospect of a very profitable deal comes your way it is permitted to sell the merchandise unobtrusively on Chol ha'Mo'ed and you shall subsequently spend some of the money on Yom Tov purchases that you otherwise may not have bought. (Shulchan Aruch OC 539:1)
The prohibition of commerce is because commerce is an arduous task. The prohibition of commerce applies also to using a Nochri as an agent to buy and sell for you. (Mishnah Berurah and Bi’ur Halachah )