Ill randomly post any creations I have made that I believe are useful or are just good time wasters.

1. Handheld Plasma Gun: https://powdertoy.co.uk/View.html?ID=8079 (Very good time waster)

2. Large Plasma Cannon: https://powdertoy.co.uk/View.html?ID=8275 (Same as my plasma gun just alot bigger)

3. Flamethrower: https://powdertoy.co.uk/View.html?ID=9268 (A simple flamethrower modeled after the plasma gun)

4. Useful Coolers and a Heater: https://powdertoy.co.uk/View.html?ID=8031 (A couple of useful heatsinks and a heater)

More to come and all of these creations can be modified or used in your own creations.

Haven't had much time to make anything but I have these two new things to add which are these two Neutron Reactors:

Large: A somewhat large Neutron reactor that creates a fairly large amount of energy from a single neutron or photon with two dual, remotely activated neutron sources which can be activated and deactivated at will either starting or stopping the reaction.
Also even after both sources have stopped feeding neutrons to the core some may linger generating pulses everytime they impact the central coil until they disappear.

Small: Similar to the large reactor only much smaller but with less efficiency as the sources are smaller and the neutrons they generate
disappear much quicker making it a better choice if you don't want the reactor to randomly generate pulses after you have stopped the flow of neutrons like the larger one does.

The outputs of both reactors have a diode on them to avoid feedback to the core which could damage it.
Just type this in the search bar "user:Time_WasterX" while in the Powder Toy and you should see them among the various other things I have made.

Just made a bunch of quick charge but slow discharge batteries:
1:A quick charge and quick discharge battery that charges in 2 seconds to charge and takes 12 seconds at 50fps to discharge completely.
Good for creating a steady flow of electricity from power sources that produce purely random pulses.

2:A quick charge and slow discharge battery that is large and takes 5 seconds to charge and 1min 30sec to discharge completely at 50fps.
Good for something that requires a slow discharging battery like a clock or anything.

3:A quick charge battery that is tall and slim resembling a AAA that takes 4 seconds to charge and 1min to discharge at 50fps.
Same uses as bigger one just slimmer and smaller and with the loss of 30sec of discharge time.

All can be found by searching "user:Time_WasterX" and they will be in the list of creations that come up.