As has been suggested in many other similar threads, Pencil offers you a nice framework for prototyping and wireframing (even web stuff). And it's free.
I realise you've already said this isn't the answer you're looking for (having been linked to my question on the topic) but my scope is web development... Which is what you say you want to do. It's perfect for fleshing out page-level objects in a quick grid layout. Much more simple than a full graphics package, with various UI hints available as drag-on objects.
As was mentioned above WireframeSketcher wireframing tool is also available on Ubuntu. Recently I started providing a standalone version so it's not Eclipse only anymore. Give it a try.
I see you mention "internet sites". For web interface mockups, I like to use gomockingbird.com.
It's very quick and web-based, so it will definitely work in Ubuntu. You could probably use it for software application interface development, as well.
I've been playing with Pencil, it's a good program, but I couldn't get any export function to work and I didn't like the program starting a firefox process. In the other hand, I also tried balsamiq mockups, really nice program as well but I ended up sick because they use Adobe Air to make the program available for all platforms, and you already know that Adobe Air doesn't support Linux anymore. Finally I tried Wireframesketcher, I installed it in a few seconds, with an integrated Ubuntu inferface. It's very intuitive and it has got all the features I was looking for. Very powerful program.
You can always use Inkscape to create a few shapes and be very flexible. Just need to get the basics of Inkscape geometry stuff down for precise positioning of elements and you're good to go, almost unlimited possibilities. Once you've created a nice little palette, you just copy paste and align elements. Whenever you need something new, it's usually not too hard to add.
As has been suggested in many other similar threads, Pencil offers you a nice framework for prototyping and wireframing (even web stuff). And it's free.
I realise you've already said this isn't the answer you're looking for (having been linked to my question on the topic) but my scope is web development... Which is what you say you want to do. It's perfect for fleshing out page-level objects in a quick grid layout. Much more simple than a full graphics package, with various UI hints available as drag-on objects.
There's a deb package available for installation.
As was mentioned above WireframeSketcher wireframing tool is also available on Ubuntu. Recently I started providing a standalone version so it's not Eclipse only anymore. Give it a try.
I see you mention "internet sites". For web interface mockups, I like to use gomockingbird.com.
It's very quick and web-based, so it will definitely work in Ubuntu. You could probably use it for software application interface development, as well.
If you are a professional and looking for professional application then you can try balsamiq
Download the desktop app for windows and install it via wine.
It has a 30 day trial period after which you have to buy its license with $89.
According to me it is the best one in the market.
Currently Balsamiq is the widely used program for mock ups etc in the cooperate levels. It is professional.
They have an trial version which you can download and play with. It is not FREE.
https://balsamiq.com/products/
If you are looking for an open-source GUI prototyping tool Pencil Project is recommended. It is FREE.
https://pencil.evolus.vn/
It works on
Fedora,Ubuntu,WindowsandMac OSX.Find the download page of Pencil Project.
https://pencil.evolus.vn/Downloads.html
I've been playing with Pencil, it's a good program, but I couldn't get any export function to work and I didn't like the program starting a firefox process. In the other hand, I also tried balsamiq mockups, really nice program as well but I ended up sick because they use Adobe Air to make the program available for all platforms, and you already know that Adobe Air doesn't support Linux anymore. Finally I tried Wireframesketcher, I installed it in a few seconds, with an integrated Ubuntu inferface. It's very intuitive and it has got all the features I was looking for. Very powerful program.
You can always use
Inkscapeto create a few shapes and be very flexible. Just need to get the basics of Inkscape geometry stuff down for precise positioning of elements and you're good to go, almost unlimited possibilities. Once you've created a nice little palette, you just copy paste and align elements. Whenever you need something new, it's usually not too hard to add.