Note: It's only tilesets for now, but knowing myself, there will be other things to come. //Addendum: After the release of MV it's less likely, though
Terms of Use:
The edits are free to use for non-commercial and commercial projects as long as credit is given.
You need to own RPG-Maker VX ACE to use the edits made from the VX ACE RTP. Every file is edited from the VX Ace RTP unless other information is provided.
Whom to credit I specify below the respective resources.
For the tiles made from scratch, if you intend to use them commercially, I want to be contacted first. It's still free to use, it's just that I want to know where they are used.
Please do not repost these resources and instead link back to this thread if you want to share them somewhere. You can edit them for your personal use. If you want to share those edits you made, make sure everything is credited properly and provide a link back to this thread. If you tell me about it, I can also add a link to it in this post so people know where to look for resources that fit with the ones in here.
Update log:
2015-07-25: A few changes to the Terms of Use. New edits in "Recolours & Edits" (A1, A2, A4, A5 and B-E)
2015-06-26: Minor addition to "Columnar Basalt"'s Tile A5; new edits in "Recolours & Edits" (A2, A4, A5 and B-E)
2017-07-21: Replaced image links because of a switch from Photobucket to directupload.net and changed wording that's way too outdated to reflect reality more (chances are incredibly slim that I'll be creating more Ace stuff in the near and mid-distance future)
Tilesets:
Renaissance Italy-inspired A3 walls with matching roof recolours:
Spoiler
Spoiler
Example Screenshot/Testmap (with RTP tiles on it):

Tile A2:

Tile A4:

Tile A5:

Tile C:

Info regarding the top right Tile C tiles: Those are the upper layers of what you can find on Tile A5.
The columnar basalt tiles are painted from scratch, so credit Chiara if you use only those.
The green details are either edited or colour-picked from the RTP; and there are some ground tile recolours on A2 and A5; for those, credit both Enterbrain and Chiara.
Info: Candacis has a water autotile and grass+ground autotile that fits with my grass recolour.

Tile A2:

Tile A4:

Tile A5:

Tile C:

Info regarding the top right Tile C tiles: Those are the upper layers of what you can find on Tile A5.
The columnar basalt tiles are painted from scratch, so credit Chiara if you use only those.
The green details are either edited or colour-picked from the RTP; and there are some ground tile recolours on A2 and A5; for those, credit both Enterbrain and Chiara.
Info: Candacis has a water autotile and grass+ground autotile that fits with my grass recolour.
Spoiler
Tile A1:

Meant to be a shallow, muddy water tile. You need to own RPG-Maker XP to use this autotile since I used parts of the XP beach water autotile for this.
Tile A2:

Here, I wanted to have the sand's colour and value look similar to the XP RTP one's and tried to have the grass match the new colour better, same goes for the cliff edits on Tile A4.
For the other ground tile recolour, I wanted to save space. They can be either shift-clicked or placed on Tile A5.

Recolour of the green carpet and the marble-ish tile from A5; extracted the carpet pattern and used it to make decorative floor tiles (I love that pattern).

My grass recolour combined with marble-ish borders (forgive the filename, I forgot to rename it once I remembered the correct word).

One recolour, one edit, and one edit which is pretty much a recolour with reduced texture.
Tile A4:


The two on the left are recolours I made about one year ago, the one on the right is overpainted to remove the bolts.

Wall tiles painted from scratch.
Tile A5:

One recolour plus stairs made of the recoloured carpet. Also added stairs for going down for both.
Update 2015-07-25: Added marble-ish stairs plus versions with decorative element.

Floor tiles painted from scratch with colour variations.
Tile B-E:

Changed the book cover (the RTP one is read from right to left it seems), added a few more muted colours, same goes for the books on the bookshelves. Oh, and I edited the teecup to have a larger mug (can also be used for coffee).
Empty map to paint your own landmasses on. For the beds, I added the other beds' blankets to this one and tried to have them match the first one's in hue and value as closely as possible.
The plushie is an overpaint of the teddy bear, yellow flowers are randomly painted into the box.

Edits of the book shelves and an additional bed. The bottles are painted from scratch.

Vertical beds with a few variations.

The bottles painted from scratch with more variety. Those are not arranged in any tileset format!
For these, credit Enterbrain and Chiara. For those that say "painted from scratch" only credit Chiara. Check the comments below each image for additional credits and requirements.

Meant to be a shallow, muddy water tile. You need to own RPG-Maker XP to use this autotile since I used parts of the XP beach water autotile for this.
Tile A2:

Here, I wanted to have the sand's colour and value look similar to the XP RTP one's and tried to have the grass match the new colour better, same goes for the cliff edits on Tile A4.
For the other ground tile recolour, I wanted to save space. They can be either shift-clicked or placed on Tile A5.

Recolour of the green carpet and the marble-ish tile from A5; extracted the carpet pattern and used it to make decorative floor tiles (I love that pattern).

My grass recolour combined with marble-ish borders (forgive the filename, I forgot to rename it once I remembered the correct word).

One recolour, one edit, and one edit which is pretty much a recolour with reduced texture.
Tile A4:


The two on the left are recolours I made about one year ago, the one on the right is overpainted to remove the bolts.

Wall tiles painted from scratch.
Tile A5:

One recolour plus stairs made of the recoloured carpet. Also added stairs for going down for both.
Update 2015-07-25: Added marble-ish stairs plus versions with decorative element.

Floor tiles painted from scratch with colour variations.
Tile B-E:

Changed the book cover (the RTP one is read from right to left it seems), added a few more muted colours, same goes for the books on the bookshelves. Oh, and I edited the teecup to have a larger mug (can also be used for coffee).
Empty map to paint your own landmasses on. For the beds, I added the other beds' blankets to this one and tried to have them match the first one's in hue and value as closely as possible.
The plushie is an overpaint of the teddy bear, yellow flowers are randomly painted into the box.

Edits of the book shelves and an additional bed. The bottles are painted from scratch.

Vertical beds with a few variations.

The bottles painted from scratch with more variety. Those are not arranged in any tileset format!
For these, credit Enterbrain and Chiara. For those that say "painted from scratch" only credit Chiara. Check the comments below each image for additional credits and requirements.
Addendum, 2017: Here I used to say that there will be more to come (which was kind of true, I found some WIPs I might or might not finish one day), but after the release of MV I moved to it, so chances are very slim.















