When I buy anything new I don't like to just throw away the old item unless it isn't usable.
Would it be considered strange or bad mannered to take my unwanted items in to work and ask colleagues if they would like them?
An example would be a sugar bowl which was never used but replaced due to it not fitting in with our current scheme.
For somewhat work related items, I have seen people put the stuff on a table with a sign that read something like "Free to a good home." These are things like programming books etc. that they do not need anymore. However, work is not a thrift store, and I think it would be frowned upon to bring in home goods in that way. Instead find a nice place to donate it around you or a website that specializes it peer to peer local items.
Keep your work life professional.
In my experience (tech companies of various sizes, US):
Things that are work-related and still useful (books, laptop bags, keyboards, etc) are offered fairly routinely. People either leave it in the lunchroom with a note or keep it at their desks and send email. Items left in the lunchroom usually get removed (if not claimed) in a day or two. Don't let your unwanted items overstay their welcome in public places.
Small gadgets that are still useful (e.g. you upgraded your Roku player) can be treated similarly. Large gadgets (e.g. you upgraded your TiVo) are generally offered via email or wiki post or lunch-time conversation and brought in only if someone wants them.
Housewares and personal items (like clothing) pretty much aren't offered in most places. A coworker did once bring in a candelabra, accompanied by a note with an entertaining story about how he came to be trying to pass it along to a good home, but it was unusual. And I once brought in a new EFF t-shirt that was the wrong size for me, because the EFF is a widely-supported organization in that workplace. Exception: if your company is small and informal and has lots of people who are just getting established in life (e.g. furnishing their first apartments after graduating), this could be ok. If you don't know, though, I'd wait to see what other people do first.
Very occasionally, larger amounts of other items and larger items (like furniture) are offered via email. For example, a coworker once inherited a relative's large collection of SF paperbacks, didn't want them personally, and thought others would be interested because we talked about SF a lot. This was a "you're welcome to come to my house, look through boxes, and take away anything you like" offer. How acceptable this is correlates with how likely those specific coworkers are to be interested in the item.
Only offer to pass along things that you can reasonably believe your coworkers would find valuable. Otherwise, there are charities that will be happy to accept donations of usable items and put them to use helping other people.
This would not be normal in my experience. If in a conversation it came up that I have a sugar bowl to get rid of, then maybe I'd bring it in on request. But really it's more normal to bring in consumables.
So I often bring in avacados or bananas when my trees are ripe, since there is too much for my family to eat. One of the guys here brings in mangoes in season and stuff like that. One chap brings in home smoked fish (smoked with mango wood) on occasion but he sells it to us very cheap and has express permission to do so. But it would be weird if someone bought in knick knacks on the off chance someone wants it.
In a small company with a tight team it might be fine, and I have never seen it expressly forbidden. It's just unusual. Normally you would donate it to charity or have a garage sale, or give it to family or something, but not take it to work.
You can do it but there us a right way to do it.
Something not mentioned in other answers is how you go about advertising the item can make all the difference. Leaving it laying around with a note could be frowned upon in some environments. Leaving a item in a shared space could cause some people to get upset.
My work place and a few before have started a Buy and Sell group on what ever convenient communications platform you have. It can be a email group or what ever.
The rules are:
Opt-in only, No spam to all staff
Items can be brought in but not put on display
1 Email advertisement per-item
Exchanges are done outside of work hours
By joining Buy and Sell group you acknowledge that Company xyz is not responsible for {legal terms}
Many companies already have a mechanism for that. Some Slack channel, forum, sharepoint etc. for private employee to employee sales, trades, and give-aways. If your company is big enough I would run this suggestion by HR. It's typically a win-win, and in most cases almost free to implement
In my job it would be questionable. Down to which team you were in. At a higher level, some managers may see it as tacky but not say anything. So it could impact your reputation without you realizing it. As a co-worker, it would feel like you were dumping your junk on us. I personally think donating it would be best. And, if nothing else, you could put down your donation when you file your taxes. If you honestly think someone may be interested at your work, I suggest taking a photo with your smartphone and only email it out to co-workers you are close with, adding the note that they can pass it along to anyone they think may be interested. Important: Explain what condition it is in. And more importantly why you no longer want it yourself. Strongly suggest you do NOT have a table where people can just leave things to give away to whomever wants it. It gets tacky real quick and can become a dumping ground. Plus we have clients that sometimes come to our floor and that isn't something that looks professional. Again, this boils down to what company you work for, how client-facing is your floor, what your immediate team is like, how your manager would perceive this, etc. Doing this might unknowingly impact your reputation at work, whether it is fair or not.
